Log Message:
Add an emacs meta-package. This will install your preferred emacs based
on EMACS_TYPE.

It does some moderately unclean things with versions and PKGREVISION so
that updating should work seamlessly -- this package should end up with
the same PKGNAME (emacs) and the same version (24.2, 23.4, etc.) and
one PKGREVISION higher than the previously existing emacs packages.