group admin no longer exists on new precise install

...so let's just use the default puppet-git group (this seems fairly sensible)
when setting up ownership.
nit! whitespace
the "administrative user group" changed from admin to sudo, so prefer sudo

We want to use the sudo when it exists and admin as a fallback, but when both
exist we should prefer sudo.

*sigh*
also, address git vs git-core by allowing either to satisfy our dependency

All these crazy changes...  it's almost like we're going between two LTS
releases or something!
Merge pull request #14 from RsrchBoy/topic/precise-dpkging

Prefer 'sudo' group when it exists; alow either git or git-core to satisfy us