bug#11603: Rename "configure.in" to "configure.ac"

Tags: patch

Here's a patch I'd like to install into the trunk
after a bit more testing, to future-proof Emacs
against the next version of Autoconf.

=== modified file 'ChangeLog'
--- ChangeLog	2012-06-01 18:26:21 +0000
+++ ChangeLog	2012-06-01 19:23:46 +0000
 <at>  <at>  -1,5 +1,15  <at>  <at> 
 2012-06-01  Paul Eggert  <eggert <at> cs.ucla.edu>

+	Rename configure.in to configure.ac.
+	The name 'configure.in' has been obsolescent for quite some time,
+	and the next release of Autoconf will generate warnings for it.
+	* configure.ac: Rename from configure.in.
+	* INSTALL, INSTALL.BZR, README, make-dist:
+	* Makefile.in (AUTOCONF_INPUTS):
+	* autogen.sh (autoconf_min):
+	* autogen/update_autogen (sources):
+	Adjust to reflect new name.
+
 	Remove --disable-maintainer-mode option from 'configure'.  (Bug#11555)
 	It is confusingly named and rarely useful.  See, for example,
 	<http://lists.gnu.org/archive/html/emacs-devel/2011-12/msg00089.html>.

=== modified file 'INSTALL'
--- INSTALL	2012-04-17 21:40:07 +0000
+++ INSTALL	2012-06-01 19:23:46 +0000
 <at>  <at>  -676,9 +676,9  <at>  <at>