Solved with a simple shader templating mechanism and string replacements
of the necessary sampler types/texture accesses and texture coordinate
mangling for rectangular and external-oes textures.
Add the various tokens/strings for the differnet texture types (2D, rect, oes)
Changes the GLmemory api to include the GstGLTextureTarget in all relevant
functions.
Update the relevant caps/templates for 2D only textures.
Use base class default method instead of only copying flags and
timestamp. This way, selected meta's like compostion overlay will
be passed downstream as expected.
https://bugzilla.gnome.org/show_bug.cgi?id=754047
During allocation query, when this element is not passthrough, it must
relay the overlay compostion meta and it's parameters. Fortunatly, base
transform can do this for us.
https://bugzilla.gnome.org/show_bug.cgi?id=753850
