Remove assumption in test about ~/.gitconfig

Both user.email and user.name are required for this test to run properly.
These values might not be available on automated build systems. Removal of this assumption allows testing in a chroot without modifications to the chroot.
Alternatively all 4 of GIT_{AUTHOR,COMMITTER}_{NAME,EMAIL} can be set.
Rename libexec to lib

Debian does not provide a libexec, needed for #49.
Add debian packaging