Support haskell_proto_library

[judah]

haskell_proto_library rules don't get loaded correctly in the interpreter, either directly or as dependencies:

$ hrepl hrepl/tests:ProtoLib
hrepl: ...f/execroot/hrepl/bazel-out/k8-fastbuild/bin/hrepl/tests/test_haskell_pb.HaskellLibrary.pb: openBinaryFile: does not exist (No such file or directory)
$ hrepl hrepl/tests:test_haskell_pb
hrepl: ...f/execroot/hrepl/bazel-out/k8-fastbuild/bin/hrepl/tests/test_haskell_pb.HaskellCompile.pb: openBinaryFile: does not exist (No such file or directory)