Fix the build system to use MPM_SUBDIR_NAME (which points to the directory
with the MPM in) instead of MPM_NAME (which returns the name of the MPM);
they differ since the MPM is in experimental/.

Index: httpd-2.0.55/server/mpm/experimental/itk/config.m4
===================================================================
--- httpd-2.0.55.orig/server/mpm/experimental/itk/config.m4
+++ httpd-2.0.55/server/mpm/experimental/itk/config.m4
@@ -1,3 +1,3 @@
 if test "$MPM_NAME" = "itk" ; then
-    APACHE_FAST_OUTPUT(server/mpm/$MPM_NAME/Makefile)
+    APACHE_FAST_OUTPUT(server/mpm/$MPM_SUBDIR_NAME/Makefile)
 fi