export isl_access_info_free

export isl_access_info_free

It was thought before that there was no need to export this function,
because it is called implicitly by isl_access_info_compute_flow,
but if some error occurs in the application before the call
to isl_access_info_compute_flow, isl_access_info_free should be
called to free the (partially constructed) isl_access_info.

Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>