TMI: local git repositories

Right now, I'm solely working on getting rid of the sporadic github connectivity errors in the rustpkg test suite. That means changing the tests to create a local github repo, and then changing the behavior of rustpkg build to (when given a local repo) clone it into the first workspace in RUST_PATH, then build that copy.

It's finicky, just getting all this automation of command-line stuff to work and making sure I'm not getting confused about which directories are which. Also, still emerging from the fog resulting from the four-day weekend.