configure: updates to quiet obsolete macro warnings

Clears autoconf warnings:

configure.ac:38: warning: The macro 'AC_PROG_LIBTOOL' is obsolete.
configure.ac:38: You should run autoupdate.
aclocal.m4:3515: AC_PROG_LIBTOOL is expanded from...
configure.ac:38: the top level
configure.ac:68: warning: The macro 'AC_HELP_STRING' is obsolete.
configure.ac:68: You should run autoupdate.
./lib/autoconf/general.m4:204: AC_HELP_STRING is expanded from...
configure.ac:68: the top level
configure.ac:78: warning: The macro 'AC_HELP_STRING' is obsolete.
configure.ac:78: You should run autoupdate.
./lib/autoconf/general.m4:204: AC_HELP_STRING is expanded from...
configure.ac:78: the top level

libtoolize: Consider adding 'AC_CONFIG_MACRO_DIRS([m4])' to configure.ac,
libtoolize: and rerunning libtoolize and aclocal.
libtoolize: Consider adding '-I m4' to ACLOCAL_AMFLAGS in Makefile.am.