Revert all the work that happened on the master branch.
Sadly, this is the only way to merge the current development branch back
into master.
It is now abundantly clear that I merged the 1.99 branch far too soon,
and that Clutter 2.0 won't happen any time soon, if at all.
Since having the development happen on a separate branch throws a lot of
people into confusion, let's undo the clutter-1.99 → master merge, and
move back the development of Clutter to the master branch.
In order to do so, we need to do some surgery to the Git repository.
First, we do a massive revert in a single commit of all that happened
since the switch to 1.99 and the API version bump done with the
89a2862b05 commit. The history is too long
to be reverted commit by commit without being extremely messy.
Acquiring the Clutter lock to mark critical sections is not portable,
and not recommended to implement threaded applications with Clutter.
The recommended pattern is to use worker threads, and schedule UI
updates inside idle or timeout handlers within the main loop. We should
enforce this pattern by deprecating the threads_enter()/leave()
functions. For compatibility concerns, we need internal API to acquire
the main lock during frame processing dispatch.
https://bugzilla.gnome.org/show_bug.cgi?id=679450
