Build Fix -- compatibility issue with newer autoconf

Build Fix -- compatibility issue with newer autoconf

Whan running ./autogen.sh it failed on _SXE_CHECK_LT2, it complained that
AC_CONFIG_MACRO_DIR can only be called once.

Using AC_CONFIG_MACRO_DIRS instead fixes the issue as that particular
macro is designed to be called multiple times.

	* configure.ac: Use AC_CONFIG_MACRO_DIRS instead of
	AC_CONFIG_MACRO_DIR.

	* m4/sxe-libtool.m4 (_SXE_CHECK_LT2): Ditto.

Reported-by: Arthur Miller <arthur.miller@live.com>:
Signed-off-by: Steve Youngs <steve@sxemacs.org>