As with the git.t split, split these into files corresponding to the library being tracked. Fold the signature tests into the commit test script to match upstream.
The single git.t file is not well named, and a lot of unrelated tests are included in the same file. However internally it is well structured, so perhaps it makes more sense to structure it along the lines of the libgit2 library. This is a simple split of the git.t file into four separate tests. The signature tests are included in 04-commit.t, but we'll move them to 04-signature.t for the moment.
These changes are also why the libgit2 package is yet to be accepted into Debian.
The tests failed when the upstream library rearranged its constants; but the value is not an API feature, so we shouldn't depend on it but instead test that error conditions return the right constant by triggering those errors.