[[ Bug 10990 ]] Make sure MCTileCacheDeactivate is called on the system thread on iOS, otherwise textures are not freed.
[[ Bug 10991 ]] Ensure that we don't force flush the supertile list at the start of tiling (otherwise all tiles are flushed after a compact!).
Merge branch 'bugfix-10990' into release-6.1.0
Merge branch 'bugfix-10991' into release-6.1.0