use correct autoconf macro name AC_CONFIG_MACRO_DIR without trailing S is known by autoconf since 2.58. AC_CONFIG_MACRO_DIR with trailing S is known by autoconf newer than 2.69. This fixes libtool after 'autoreconf -fi'. Fixes commit a8a65c7f6c6b6463bbdee119c0ff71536925e455 Related to issue #145 Signed-off-by: Olaf Hering <olaf@aepfle.de>