TMI: tests passing is a good feeling, though...

I finally fixed all the fallout from changing rustpkg to use the target rustpkg instead of the host rustpkg in the tests (if you understood that sentence, congratulations). So tomorrow, I can actually get back to making rustc itself understand extern mod a = b/c/d/;.

In the background, worked a little more on making rustpkg understand tags that aren't version numbers. After talking to Graydon, we won't support branches after all; just tags. If a tag doesn't look like a version number, we'll match on it exactly rather than treating it as a number that can be compared with other versions.