Recompile .proto files with gpb also with prefix/suffix

For protocol buffer files, when there were gpb options to alter the
module name with prefix or suffix, recompilation was not properly
detected. This is now fixed. (Issue #384).

Properly detecting change meant moving from rebar_base_compiler, so it
also meant processing protocol buffer files in sequence instead of in
parallel.
Merge pull request #386 from tomas-abrahamsson/gpb-recompilation-detection

Recompile .proto files with gpb also with prefix/suffix