A few porting etc. fixes for the new file monitor code.

A few porting etc. fixes for the new file monitor code.

See the thread containing
<http://lists.gnu.org/archive/html/emacs-devel/2013-06/msg00109.html>.
* gfilenotify.c (dir_monitor_callback, Fgfile_add_watch)
(Fgfile_rm_watch): Don't assume EMACS_INT is the same width as a pointer.
(dir_monitor_callback, Fgfile_rm_watch):
Use assq_no_quit instead of Fassoc, for speed.
(dir_monitor_callback, Fgfile_rm_watch):
eassert that the monitor is a fixnum.
(dir_monitor_callback): No need for CDR_SAFE.
Simplify building of lisp with alternative tails.
(Fgfile_add_watch, Fgfile_rm_watch):
Do not assume glib functions set errno reliably on failure.
(Fgfile_add_watch): Check that the monitor survives the XIL trick,
and signal an error otherwise.
(Fgfile_rm_watch): Prefer CONSP to !NILP.
Use Fdelq instead of Fdelete, for speed.