Implementation of ST_AsBinary for RASTER type

[mloskot]

This is just a record of the plan I've made to start implementing ST_AsBinary function for WKT Raster. The function is listed in the big plan.

The first version of ST_AsBinary I'm going to implement will do nearly the same what ST_byte function does. It's prototype is:

bytea ST_AsBinary(raster r1);

At the moment, I don't aim to implement compression support, but later it can be extended to provide it:

bytea ST_AsBinary(raster r1, text compression);