Improve kill-ring-deindent-mode

* etc/NEWS:
* lisp/simple.el (kill-ring-deindent-buffer-substring-function):
(kill-ring-deindent-mode): Deindent by the column number at BEG
in lieu of the indentation at BEG.

etc/NEWS

@@ -148,8 +148,8 @@ right-aligned to is controlled by the new user option
 ---
 ** New global minor mode 'kill-ring-deindent-mode'.
 When enabled, text being saved to the kill ring will be de-indented by
-the number of columns its first line is indented.  For example,
-saving the entire function call within:
+the column number at its start.  For example, saving the entire
+function call within:
 
 foo ()
 {

lisp/simple.el

@@ -11150,13 +11150,13 @@ seconds."
 Maybe delete it if DELETE is non-nil.
 
 Before saving the text, indent it leftwards by the number of
-columns of indentation at BEG."
+columns at BEG."
   (let ((a beg)
         (b end))
     (setq beg (min a b)
           end (max a b)))
   (let ((indentation (save-excursion (goto-char beg)
-                                     (current-indentation)))
+                                     (current-column)))
         (text (if delete
                   (delete-and-extract-region beg end)
                 (buffer-substring beg end))))
@@ -11170,8 +11170,8 @@ columns of indentation at BEG."
   "Toggle removal of indentation from text saved to the kill ring.
 
 When this minor mode is enabled, text saved into the kill ring is
-indented towards the left by the number of columns the line at
-the start of the text being saved is in turn indented."
+indented towards the left by the column number at the start of
+that text."
   :global 't
   :group 'killing
   (if kill-ring-deindent-mode