Fix builds with versions of automake prior to 1.13.

[igorpeshansky]

This fixes the following build error on older platforms:

./configure: line 37411: syntax error near unexpected token `$am__api_version,lt,1.12,'
./configure: line 37411: `AX_COMPARE_VERSION($am__api_version,lt,1.12,'

A bit of context for the change: older versions of automake did not automatically parse the AC_CONFIG_MACRO_DIR directive, so we have to explicitly tell aclocal to find extra macros there. Also, running libtoolize before aclocal ensures that the libtool macros have been copied into m4 for aclocal to find (otherwise it would sporadically use the libtool macros that came with whatever version of automake was installed, rather than those supplied by libtool itself).

[bmoyles0117]

LGTM