try building the offline extension by default now that the installer is hooked up to install it

as an optional component. Eventually we may hook this up to a build flag.

mail/extensions/Makefile.in

@@ -26,7 +26,7 @@ VPATH		= @srcdir@
 
 include $(DEPTH)/config/autoconf.mk
 
-DIRS = 
+DIRS = offline
 
 ifdef MOZ_PSM
 BUILD_SMIME=1