[GRASS5] 5.3.0 release

[Paul Kelly]

Hello
I was thinking if the 5.3.x series is going to be identifiably separate
from the 5.0.x series, we might as well go ahead and remove the internal
copy of PROJ that is in GRASS and make an external PROJ installation an
absolute requirement. This was discussed before and I thought it might not
be a good idea to suddenly introduce the requirement but it would be OK in
the context of 5.3/5.4. Would make the source code package smaller as
well.

Some features such as NTv2 grid transformations are only supported in the
latest PROJ.4.4.7 and not in the private GRASS copy of PROJ.

Maybe the GDAL bridge code could be removed as well and r.in.gdal not
compiled unless GDAL was available at compilation time. Just in general
this would make the linkage to external libraries cleaner I feel.

Are there any objections? I might not be able to finish the PROJ part for
a week or two though if it is going ahead.

Paul