Fixes issue protocolbuffers#552. (And yay, it looks like our build profile supports this...)

Move _conformance directory to conformance. (The _ was apparently there
to prevent "go install ./..." from touching that directory, which
doesn't seem like a sufficient reason to have a weird path name.)

Delete conformance_proto directory, regenerate the proto at test time.
(This proto is used for communications between the test runner and test
process; nothing else needs it.)

Add a list of known failures.

Add a Makefile so that "make test" in the conformance directory does the
right thing. (Requires that github.com/google/protobuf be installed
somewhere.) Include documentation in "make all" output. Skip tests if
the necessary dependencies don't exist.

…60849

Internal change

…60849

Internal change