try to make freeswitch build with a little older autoconf

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@2030 d0543943-73ff-0310-b7d9-9358b9ac24b2

configure.in

 #                                               -*- Autoconf -*-
 # Process this file with autoconf to produce a configure script.
 
-AC_PREREQ(2.59)
+AC_PREREQ(2.57)
 AC_INIT(FULL-PACKAGE-NAME, VERSION, BUG-REPORT-ADDRESS)
 AC_CONFIG_AUX_DIR(build/config)
 AM_INIT_AUTOMAKE(libfreeswitch,0.1)