doc change for regex.m4

[Jim Meyering]

I've had this change sitting around for a while...

        * m4/regex.m4: Update the description of the configure-time option,
        --without-included-regex, to state accurately what the defaults are,
        and perhaps to give people an idea why using this option is risky.

Index: m4/regex.m4
===================================================================
RCS file: /sources/gnulib/gnulib/m4/regex.m4,v
retrieving revision 1.63
diff -u -p -r1.63 regex.m4
--- m4/regex.m4 15 Feb 2007 00:16:55 -0000      1.63
+++ m4/regex.m4 24 Feb 2007 11:52:48 -0000
@@ -1,4 +1,4 @@
-#serial 45
+#serial 46

 # Copyright (C) 1996, 1997, 1998, 1999, 2000, 2001, 2003, 2004, 2005,
 # 2006, 2007 Free Software Foundation, Inc.
@@ -18,9 +18,12 @@ AC_DEFUN([gl_REGEX],

   AC_ARG_WITH([included-regex],
     [AC_HELP_STRING([--without-included-regex],
-                   [don't compile regex; this is the default on
+                   [don't compile regex; this is the default on 32-bit
                     systems with recent-enough versions of the GNU C
-                    Library (use with caution on other systems)])])
+                    Library (use with caution on other systems).
+                    On systems with 64-bit ptrdiff_t and 32-bit int,
+                    --with-included-regex is the default, in case
+                    regex functions operate on very long strings (>2GB)])])

   case $with_included_regex in #(
   yes|no) ac_use_included_regex=$with_included_regex