use the AC_PREFIX_DEFAULT macro to set the default prefix instead of setting

the variable directly, so that the configure --help information shows the
correct default prefix


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@35391 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configure

@@ -1,5 +1,5 @@
 #! /bin/sh
-# From configure.ac Revision: 33953 .
+# From configure.ac Revision: 33995 .
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.59e.
 #
@@ -566,6 +566,8 @@ PACKAGE_BUGREPORT=
 
 ac_unique_file="asterisk"
 ac_unique_file="asterisk.c"
+ac_default_prefix=/usr/local
+ac_default_prefix=/usr
 # Factoring default headers for most tests.
 ac_includes_default="\
 #include <stdio.h>
@@ -2023,10 +2025,10 @@ ac_config_headers="$ac_config_headers include/asterisk/autoconfig.h"
 
 case "${host}" in
      *freebsd*)
-     ac_default_prefix=/usr/local
+
      ;;
      *)
-     ac_default_prefix=/usr
+
      if test ${sysconfdir} = '${prefix}/etc'; then
         sysconfdir=/etc
      fi