CoglClipStacks can now be reference counted via a CoglHandle. The ClipClipState now stores handles in the list rather than CoglClipStack pointers.
CoglClipStackState has now been renamed to CoglClipState and is moved to a separate file. CoglClipStack now just maintains a stack and doesn't worry about the rest of the state. CoglClipStack sill contains the code to flush the stack to GL.