The addition of method implementations in the base class in the
plugin-gobject branch broke the logic for checking to see
if a plugin didn't implement an effect. Requiring a mandatory
chain up to the base class is a fiddly anyways, so this patch
does the 'running' count computations in a different (and more
robust) way.
mutter-plugin.h mutter-plugin.c: Add _mutter_plugin_effect_started()
to increment the running count.
mutter-plugin-manager.c: Call _mutter_plugin_effect_started()
as necessary.
mutter-plugin.c: Remove the "real" methods that did nothing
but implement the runnning count.
plugins/default.c: Remove chain-ups.
