[cogl-texture-2d-sliced] allow COGL_FORMAT_ANY with _new_with_size()
[cogl-texture-2d-sliced] allow COGL_FORMAT_ANY with _new_with_size()

It's useful when initialzing offscreen draw buffers to be able to ask
Cogl to create a texture of a given size and with the default internal
pixel format.

djdeath/cogl,collects/cogl,gcampax/cogl,djdeath/cogl,Distrotech/cogl,spatulasnout/cogl,djdeath/cogl-android,gcampax/cogl,collects/cogl,Distrotech/cogl,djdeath/cogl-android,gcampax/cogl,gcampax/cogl,djdeath/cogl-android,Distrotech/cogl,Distrotech/cogl,spatulasnout/cogl,djdeath/cogl