St cache texture destroy fixes
The texture cache seems not to use the destroy notify functions properly in some cases.
Another option for the first commit would be adding a wrapper for cogl_object_unref
but I'm not sure there's a point in adding a NULL texture to the cache anyway.
Otherwise both the issues could be fixed by using a single map with some smarter DestroyNotify, but I imagine it's just over-engineering.
Fixes #210 (closed)
Edited by Marco Trevisan