fix bugs in C++ protobuf_load/protobuf_dump

add a C++ level sanity check in test_protobuf
add more examples of shared values for NIW
grab assert_close from loom, and fill out more specializations

this allows test_protobuf to assert for actual load/dump correctness,
instead of just checking for runtime crashes
Merge pull request #77 from stephentu/baseline

fix bug in NIW templated protobuf_load()/protobuf_store()