[3025] Don't use # character in m4 messages

This has caused issues in the past (see other error messages for example),
and escaping with \ doesn't seem to help in those cases.

configure.ac

@@ -916,7 +916,7 @@ if test "$BOOST_OFFSET_PTR_OLD" = "yes" -a "$use_shared_memory" = "yes" ; then
     AC_MSG_ERROR([You're trying to compile against boost older than 1.48 with
 shared memory. Older versions of boost have a bug which causes segfaults in
 offset_ptr implementation when compiled by GCC with optimisations enabled.
-See ticket #3025 for details.
+See ticket no. 3025 for details.
 
 Either update boost to newer version or use --without-shared-memory.
 Note that most users likely don't need shared memory support.