Teach the inanity 'bot about protobuf-related files

With the addition of protobuf support, we can now expect *.proto files to show up in source trees, if only as test data; these are source files that should probably be subject to at least some of our usual checks for source files (except for test data in tests/.*/data/ directories, as ever).

From these we generate *.cpp files that start with the header line

/* This file is autogenerated. DO NOT CHANGE. All changes will be lost */

which is not currently matched by the inanity 'bot check for generated files; we should add that to its vocabulary.