* acinclude.m4: New file.  Contains `libtool.m4' from libtool-1.2,
the version from which glib's libtool forked.  Needed for people
who use post-1.2 alphas of libtool.
* configure.in (enable_mem_check, enable_mem_profile): Replace
`echo -n' with AC_MSG_CHECKING.
(fd_set): Explain test for `fd_set' better.