autotools: rename configure.in to configure.ac

configure.in is deprecated since long and will be replaced by
configure.ac. For more information, see:
  http://lists.gnu.org/archive/html/automake/2012-08/msg00023.html

configure.ac

@@ -1,6 +1,6 @@
 #TODO A better place for default CFLAGS?
 
-AC_INIT(configure.in)
+AC_INIT(configure.ac)
 
     AM_CONFIG_HEADER(config.h)
     AM_INIT_AUTOMAKE(suricata, 1.3dev)
@@ -1315,4 +1315,3 @@ echo "To install Suricata into /usr/bin/suricata, have the config in
 /etc/suricata and use /var/log/suricata as log dir, use:
 ./configure --prefix=/usr/ --sysconfdir=/etc/ --localstatedir=/var/"
 echo
-