document M4 variable

[Eric Blake]

I have been patching some core dumps in m4 1.4.4, and wanted to
test my version with autoconf.  To my relief, setting M4=/my/m4
worked to override which m4 was used, even though it wasn't
documented.  But I propose this to make it obvious:

2006-06-03  Eric Blake  <address@hidden>

        * bin/autoreconf.in (help): Document M4 environment variable.
        * bin/autoconf.as (Usage): Likewise.
        * bin/autom4te.in (help): Likewise.
        * doc/autoconf.texi (autom4te Invocation): Likewise.

Index: bin/autoconf.as
===================================================================
RCS file: /sources/autoconf/autoconf/bin/autoconf.as,v
retrieving revision 1.18
diff -u -p -r1.18 autoconf.as
--- bin/autoconf.as     25 Apr 2006 12:57:28 -0000      1.18
+++ bin/autoconf.as     4 Jun 2006 02:15:48 -0000
@@ -45,7 +45,7 @@ Warning categories include:
   \`none'          turn off all the warnings
   \`error'         warnings are error
 
-The environment variable \`WARNINGS' is honored.
+The environment variables \`M4' and \`WARNINGS' are honored.
 
 Library directories:
   -B, --prepend-include=DIR  prepend directory DIR to search path
Index: bin/autom4te.in
===================================================================
RCS file: /sources/autoconf/autoconf/bin/autom4te.in,v
retrieving revision 1.97
diff -u -p -r1.97 autom4te.in
--- bin/autom4te.in     6 Jan 2006 00:10:37 -0000       1.97
+++ bin/autom4te.in     4 Jun 2006 02:15:48 -0000
@@ -191,7 +191,7 @@ Languages include:
 
 " . Autom4te::ChannelDefs::usage . "
 
-The environment variable \`WARNINGS\' is honored.
+The environment variables \`M4\' and \`WARNINGS\' are honored.
 
 Library directories:
   -B, --prepend-include=DIR  prepend directory DIR to search path
Index: bin/autoreconf.in
===================================================================
RCS file: /sources/autoconf/autoconf/bin/autoreconf.in,v
retrieving revision 1.133
diff -u -p -r1.133 autoreconf.in
--- bin/autoreconf.in   18 May 2006 06:50:35 -0000      1.133
+++ bin/autoreconf.in   4 Jun 2006 02:15:48 -0000
@@ -89,7 +89,7 @@ Library directories:
   -I, --include=DIR          append directory DIR to search path
 
 The environment variables AUTOCONF, AUTOHEADER, AUTOMAKE, ACLOCAL,
-AUTOPOINT, LIBTOOLIZE are honored.
+AUTOPOINT, LIBTOOLIZE, M4 are honored.
 
 Report bugs to <address@hidden>.
 ";
Index: doc/autoconf.texi
===================================================================
RCS file: /sources/autoconf/autoconf/doc/autoconf.texi,v
retrieving revision 1.1035
diff -u -p -r1.1035 autoconf.texi
--- doc/autoconf.texi   3 Jun 2006 23:21:06 -0000       1.1035
+++ doc/autoconf.texi   4 Jun 2006 02:15:53 -0000
@@ -9065,7 +9065,10 @@ autom4te @var{options} @var{files}
 @end example
 
 @noindent
-where the @var{files} are directly passed to @command{m4}.  In addition
address@hidden M4
+where the @var{files} are directly passed to @command{m4}.  By default,
address@hidden m4 is found during configure, but the environment variable
address@hidden can be set to tell @command{autom4te} where to look.  In addition
 to the regular expansion, it handles the replacement of the quadrigraphs
 (@pxref{Quadrigraphs}), and of @samp{__oline__}, the current line in the
 output.  It supports an extended syntax for the @var{files}: