Add the new MPM to the build system as an alternative to the other MPMs,
and mark it as experimental.

Index: httpd-2.0.55/server/mpm/config.m4
===================================================================
--- httpd-2.0.55.orig/server/mpm/config.m4
+++ httpd-2.0.55/server/mpm/config.m4
@@ -1,7 +1,7 @@
 AC_MSG_CHECKING(which MPM to use)
 AC_ARG_WITH(mpm,
 APACHE_HELP_STRING(--with-mpm=MPM,Choose the process model for Apache to use.
-                          MPM={beos|worker|prefork|mpmt_os2|perchild|leader|threadpool}),[
+                          MPM={beos|worker|prefork|mpmt_os2|perchild|leader|threadpool|itk}),[
   APACHE_MPM=$withval
 ],[
   if test "x$APACHE_MPM" = "x"; then
@@ -26,7 +26,7 @@ fi
 APACHE_FAST_OUTPUT(server/mpm/Makefile)
 
 MPM_NAME=$apache_cv_mpm
-if test "$MPM_NAME" = "leader" -o "$MPM_NAME" = "threadpool" -o "$MPM_NAME" = "perchild"; then
+if test "$MPM_NAME" = "leader" -o "$MPM_NAME" = "threadpool" -o "$MPM_NAME" = "perchild" -o "$MPM_NAME" = "itk"; then
   AC_MSG_WARN(You have selected an EXPERIMENTAL MPM.  Be warned!)
   MPM_SUBDIR_NAME=experimental/$MPM_NAME
 else