If we are not already building xmlextras, make sure to build it here.

r=pavlov.  (Wanted: explicit extension-dependency system.)

extensions/webdav/Makefile.in

@@ -45,7 +45,11 @@ VPATH            = @srcdir@
 include $(DEPTH)/config/autoconf.mk
 
 MODULE		= webdav
-DIRS             = public src
+DIRS            =
+ifeq (,$(filter xmlextras,$(MOZ_EXTENSIONS)))
+DIRS            += ../xmlextras
+endif
+DIRS            += public src
 
 include $(topsrcdir)/config/rules.mk