In inttest/proto_gpb, replace the external dependency to gpb, a
protocol buffer compiler, with a simple mock.
The mock provides enough of what is needed for inttest only,
which is to generate some dummy content, but with proper file names.
As a result, the increased timeout for the proto_gpb inttest should no
longer be needed (inttest/proto_gpb/retest.config), both since the
mock is now much faster to compile, and since any network bandwidth or
connectivity issues have now been eliminated.
exercises rebar/gpb integration
The bulk of these tests are written by Luis Rascão, hence he is the
author of this commit. As the committer, I have cherry-picked his two
commits 4c87bcd and ebb8182, from the feature/support_gpb_protobuf
branch in the git://github.com/lrascao/rebar repo, and have slightly
adapted it to fit this pluggable-proto-compilers-gpb branch.
Update the THANKS file
