Unbreak world (gcc47 plugin)

The installincludes target is run before "depend" target, so gtype.state
hasn't been created by the time "installincludes" is executed in stage 4.
Luckily there is a similar functionality for FILES that is executed at
the install phase, which will unbreak world (broken on previous commit).

Other headers are generated as well, so swap INCSGROUPS with FILESGROUPS
for everything to avoid having to figure which ones.  The headers are
needed at runtime, not buildtime, so this is okay.