conf: Better defaults for gettext imports

These aren't really used, but premit some testing of other modules that
import _ or ngettext from here without going through the gettext
install in the main script.
vc: Explicitly import VC plugin modules to help cx_Freeze's detection

Without this patch, the modules end up not being bundled in the
resulting libraries zip, even though the meld.vc package is explicitly
included.
setup: Include a few missing files