protobuffers know what files they will generate for zips/jars.

Preliminary support for compressed archives as sources. Currently .zips and .jars work for protobuffers. Code is fairly extensible, with generic functionality in zipped_sources such that not much code is needed in protobuf_gen (or other targets in the future).
doesn't look very private.  If you are going to treat these as transient files and want a true tmp directory, maybe follow the strategy used in testing to create a temp dir see base_test.py setUp()