protobuf-toolfile: add $PROTOBUF_BASE/bin to PATH

Signed-off-by: David Abdurachmanov <davidlt@cern.ch>
Merge pull request #155 from davidlt/protobuf-bin-to-path

[CMSSW_7_0_X] add $PROTOBUF_BASE/bin to PATH
Merge remote-tracking branch 'origin/IB/CMSSW_7_0_X/stable' into IB/CMSSW_7_0_X/devel-gcc472