Add gimplegacy-private.h to keep it separate from gimp-private.h.
The legacy code could now be removed and GimpPlugIn-ported plug-ins
would not notice.
Move all old wire code to gimplegacy.c and add wire code to
GimpPlugIn, which now talks with the GIMP core all by itself.
Add some more ASSERT_NO_PLUG_IN_EXISTS assertions to gimplegacy.c and
fix new code that was still using legacy API.
and make the places who need it dispatch between it and
_gimp_read_expect_msg() depending on whether there is a GimpPlugIn
instance. Also clean up some includes.
Instead of calling _gimp_close() and returning from both the main
plug-in loop variants, simply only return and call gimp_close() from
where both loops return to, at the end of gimp_main_internal().
Move the legacy loop code to gimplegacy.c. Also remove some more stuff
from gimp.c, old and new are now completely separate apart from one
glitch which wll go next...
Start copying all the actual wire communication to GimpPlugIn, and
move the legacy versions to gimplegacy.c.
This implies having the entire protocol code twice, but without any
if(PLUG_IN) { plug_in_stuff(); } else { legacy_stuff(); }
At the moment it is a wild mixture of old and new, but when finished
the wire code in gimplegacy.c will be entirely separate from the wire
code in GimpPlugIn, which will make it easy to g_assert() that only
one API is used by a plug-in.