The pango renderer was causing lots of override materials to be allocated
because the vertex_buffer API converts AUTOMATIC mode into REPEAT for
backwards compatibility. By explicitly setting the wrap mode to
CLAMP_TO_EDGE when creating the glyph_material then the vertex_buffer
API will leave it untouched.
This uses the G_GNUC_DEPRECATED macros to mark the
cogl_{texture,vertex_buffer,shader}_ref and unref APIs as deprecated.
Since this flagged that cogl-pango-display-list.c and
clutter-glx-texture-pixmap.c were still using deprecated _ref/_unref
APIs they have now been changed to use the cogl_handle_ref/unref API
instead.
