Merge branch 'cogl-client-matrix-stacks'

* cogl-client-matrix-stacks:
  Maintain the Cogl assumption that the modelview matrix is normally current
  Finish GLES{1,2} support for client side matrix stacks
  Explicitly make the modelview-matrix current in cogl_{rotate,transform,etc}
  Avoid casting CoglMatrix to a GLfloat * when calling glGetFloatv
  Removes need for casting const float * in _cogl_set_clip_planes
  Virtualize GL matrix operations and use a client-side matrix when GL is indirect