All the cool platforms support CLASH_DETECTION...

* configure.ac (CLASH_DETECTION): Define unconditionally.
Every platform using configure supports it.

* src/s/aix4-2.h, src/s/bsd-common.h, src/s/cygwin.h, src/s/darwin.h:
* src/s/gnu-linux.h, src/s/hpux10-20.h, src/s/template.h:
* src/s/usg5-4-common.h: Move CLASH_DETECTION to configure.

* etc/PROBLEMS: Recommend customizing create-lockfiles rather than
recompiling with CLASH_DETECTION unset.

ChangeLog

@@ -1,5 +1,7 @@
 2012-07-11  Glenn Morris  <rgm@gnu.org>
 
+	* configure.ac (CLASH_DETECTION): Define unconditionally.
+
 	* configure.ac (opsysfile): Use bsd-common on gnu systems.
 
 	* configure.ac (GNU_LIBRARY_PENDING_OUTPUT_COUNT):

configure.ac

@@ -3124,6 +3124,14 @@ dnl                                and macros for terminal control.])
 dnl    AC_DEFINE(HAVE_TCATTR, 1, [Define to 1 if you have tcgetattr and tcsetattr.])
 dnl fi
 
+dnl Every platform that uses configure (ie every non-MS platform)
+dnl supports this.  There is a create-lockfiles option you can
+dnl customize if you do not want the lock files to be written.
+dnl So it is not clear that this #define still needs to exist.
+AC_DEFINE(CLASH_DETECTION, 1, [Define if you want lock files to be written,
+  so that Emacs can tell instantly when you try to modify a file that
+  someone else has modified in his/her Emacs.])
+
 case $opsys in
   darwin | gnu | hpux* | *bsd )
     AC_DEFINE(NO_TERMIO, 1, [Define if termio.h should not be included.])

etc/PROBLEMS

@@ -1884,8 +1884,8 @@ Emacs uses symbolic links to implement file locks.  In a directory
 with +t bit, the directory owner becomes the owner of the symbolic
 link, so that it cannot be removed by anyone else.
 
-If you don't like those useless links, you can let Emacs not to using
+If you don't like those useless links, you can customize
-file lock by adding #undef CLASH_DETECTION to config.h.
+the option `create-lockfiles'.
 
 *** FreeBSD: Getting a Meta key on the console.
 

src/ChangeLog

@@ -1,5 +1,9 @@
 2012-07-11  Glenn Morris  <rgm@gnu.org>
 
+	* s/aix4-2.h, s/bsd-common.h, s/cygwin.h, s/darwin.h:
+	* s/gnu-linux.h, s/hpux10-20.h, s/template.h, s/usg5-4-common.h:
+	Move CLASH_DETECTION to configure.
+
 	* s/gnu.h: Remove file, which is now empty.
 
 	* s/gnu.h, s/gnu-linux.h:

src/s/aix4-2.h

@@ -42,7 +42,6 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
 /* Perry Smith <pedz@ddivt1.austin.ibm.com> says these are correct.  */
 #define SIGNALS_VIA_CHARACTERS
-#define CLASH_DETECTION
 
 /* Perry Smith <pedz@ddivt1.austin.ibm.com> says these are correct.  */
 #undef sigmask

src/s/bsd-common.h

@@ -60,10 +60,5 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 /* Define HAVE_SOCKETS if system supports 4.2-compatible sockets.  */
 #define HAVE_SOCKETS
 
-/* Define CLASH_DETECTION if you want lock files to be written
-   so that Emacs can tell instantly when you try to modify
-   a file that someone else has modified in his Emacs.  */
-#define CLASH_DETECTION
-
 /* Send signals to subprocesses by "typing" special chars at them.  */
 #define SIGNALS_VIA_CHARACTERS

src/s/cygwin.h

@@ -59,11 +59,6 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
     }							\
   while (0)
 
-/* Define CLASH_DETECTION if you want lock files to be written
-   so that Emacs can tell instantly when you try to modify
-   a file that someone else has modified in his Emacs.  */
-#define CLASH_DETECTION
-
 /* If the system's imake configuration file defines `NeedWidePrototypes'
    as `NO', we must define NARROWPROTO manually.  Such a define is
    generated in the Makefile generated by `xmkmf'.  If we don't

src/s/darwin.h

@@ -83,11 +83,6 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
    for process-connection-type dependent on the kernel version.  */
 #define MIN_PTY_KERNEL_VERSION '7'
 
-/* Define CLASH_DETECTION if you want lock files to be written
-   so that Emacs can tell instantly when you try to modify
-   a file that someone else has modified in his Emacs.  */
-#define CLASH_DETECTION
-
 /* Avoid the use of the name init_process (process.c) because it is
    also the name of a Mach system call.  */
 #define init_process emacs_init_process

src/s/gnu-linux.h

@@ -80,11 +80,6 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #define HAVE_SOCKETS
 
-/* Define CLASH_DETECTION if you want lock files to be written
-   so that Emacs can tell instantly when you try to modify
-   a file that someone else has modified in his Emacs.  */
-#define CLASH_DETECTION
-
 /* Here, on a separate page, add any special hacks needed
    to make Emacs work on this system.  For example,
    you might define certain system call names that don't

src/s/hpux10-20.h

@@ -36,11 +36,6 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 /* Define HAVE_SOCKETS if system supports 4.2-compatible sockets.  */
 #define HAVE_SOCKETS
 
-/* Define CLASH_DETECTION if you want lock files to be written
-   so that Emacs can tell instantly when you try to modify
-   a file that someone else has modified in his Emacs.  */
-#define CLASH_DETECTION
-
 /* Special hacks needed to make Emacs run on this system.  */
 
 /* This is how to get the device name of the tty end of a pty.  */

src/s/template.h

@@ -66,11 +66,6 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
 /* #undef subprocesses */
 
-/* Define CLASH_DETECTION if you want lock files to be written
-   so that Emacs can tell instantly when you try to modify
-   a file that someone else has modified in his Emacs.  */
-#define CLASH_DETECTION
-
 /* If the character used to separate elements of the executable path
    is not ':', #define this to be the appropriate character constant.  */
 /* #define SEPCHAR ':' */

src/s/usg5-4-common.h

@@ -51,9 +51,6 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
    constant to dimension an array.  So wire in the appropriate value here.  */
 #define NSIG_MINIMUM 32
 
-/* We can support this.  */
-#define CLASH_DETECTION
-
 /* Define HAVE_PTYS if the system supports pty devices.  */
 #define HAVE_PTYS