Provide backwards compatibilty with old pixman

The goal is to allow compilation against older pixman to ease regression
testing.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
win32: Prevent double-free of similar images

Based on a patch and analysis by Michael Henning.

When we create a similar-image surface for win32, we set up a couple of
back references from the image to the win32 surface, and vice versa. We
need to be careful when decoupling the reference cycle to avoid chasing
around the loop upon destruction. Currently we handled destroying the
similar-image via the parent win32 surface, but similar precaution is
required when destroying the surface via the similar-image.

Reported-by: Michael Henning <drawoc@darkrefraction.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=63787
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>