Define HAVE_DYNAMIC_LOADING.

This is part of a set of patches by Greg Stein.
diff --git a/acconfig.h b/acconfig.h
index 19e5f96..1dd7ac3 100644
--- a/acconfig.h
+++ b/acconfig.h
@@ -142,5 +142,8 @@
 */
 #undef HAVE_LARGEFILE_SUPPORT
 
+/* Defined when any dynamic module loading is enabled */
+#undef HAVE_DYNAMIC_LOADING
+
 
 /* Leave that blank line there-- autoheader needs it! */