Bug 1040009: Add support for comm-central applications to --enable-application in mozilla's configure.in, r=glandium, a=edmorley.

The purpose of this bug is to adjust the configure logic so that a .mozconfig
set up for comm-central can be used in the mozilla-central logic without needing
to adjust or override any commands.

--HG--
extra : amend_source : fa388484330eca8ead8b2fefe350f350ad5582e6