Bug 963073 - Merge tiling branch. r=Bas,jrmuizel,BenWa

http://hg.mozilla.org/users/bschouten_mozilla.com/tiling/summary

This work is mainly porting tiled layers to new textures, implementing
double-buffered tiles and implementing a texture client pool, to be used by
tiled content clients.

Any questions regarding this patch should go to:
Bas Schouten <bschouten@mozilla.com>
Chris Lord <clord@mozilla.com>
Nicolas Silva <nsilva@mozilla.com>

In their absence questions can be directed to:
Jeff Muizelaar <jmuizelaar@mozilla.com>
Benoit Girard <bgirard@mozilla.com>