Project.pm: tighten up is_empty check

Project.pm: tighten up is_empty check

The "kludge" to accomodate $Girocco::Config::empty_commit_message
can leave non-empty projects undetectable.

Refuse to consider them "empty" if they have more than two loose
objects (create-initial-empty-commit makes exactly two loose objects).

While still not perfect, the check for the new conditions remains
relatively fast (no external processes needed) and will correctly
return a false "is_empty" status now for "empty" projects that have
been modified outside Girocco.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>
fixup! Project.pm: tighten up is_empty check