Convert local `file:` URLs to paths before handing over to `git_clone`.

Fixes a bug where a locally-cloned remote would get a `file:` URL as it's origin URL, making the push machinery shrivel in fear.
Dot-syntaxify.
Use `-fileSystemRepresentation` here.
File reference URLs are file URLs; no need for a separate test.
Useless call; file reference URLs know how to path-ify themselves.
Test that the remote set by `+clone…` looks fine to libgit2.
De-oneline-ify.
Make `error` a local.
Add methods to create new bare and non-bare repositories to `GTTestCase`.
Test that new repos have unborn HEADs.
Define `expectSHAForRevspec` inline.
fixup! 76124812179f06bfdef209a650a9bd8733031b37
Use the clone tests from #280.
Put the newly-cloned repo in the test-case managed temporary directory.
Huh, bare clones don't checkout...