Ownership of the filename string was a bit fuzzy, with the result that
we were freeing it even though it was retained for use by __FILE__.
Clean up a number of other memory management issues with the new
quoting code, and change the stdscan implementation to one pass over
the string.
Semi-arbitrary change of the definition of escp to the beginning of
the argument sequence instead of the initiator character. This may
avoid an add in some code paths, and looks slightly cleaner to me.
We used numbers in nasm_unquote and C escapes in nasm_quote - use
numbers in both places, just in case some C compiler does something
weird with '\r' and (especially) '\n'.
Make the code a bit more consistent:
- ndig is now always a countdown, and we always to the (p > escp+1)
test to see if we got anything at all (this is to deal with stuff
like \x without a digit.)
- Add missing break; after 'v' (bug!).
- Preinitialize nval to zero.
Greatly simplify nasm_skip_string() by observing that for the purpose
of string skipping, all states other than st_backslash are equivalent
to st_start.
