uncommit: abort if an explicitly given file cannot be uncommitted (BC)
I've gotten burned several times by this in the last few days. The former tests
look simple enough, but if a good file and a bad file are given, the bad files
are silently ignored. Some commands like `forget` will warn about bogus files,
but that would likely get lost in the noise of an interactive uncommit. The
commit command aborts if a bad file is given, so this seems more consistent for
commands that alter the repository.
test-convert-git.t
test-subrepo-git.t
test-patchbomb-tls.t