config: set transfer.unpackLimit

config: set transfer.unpackLimit

We already try very hard to make sure the transfer.unpackLimit uses
a suitable value to avoid performance degradation and pushy race
conditions.

Try even harder by making sure it's added to a new project's config
and the etc/girocco config to avoid any pushes slipping through.

In particular, this catches the case of an administrator doing some
kind of "pushy" work outside the usual Girocco mechanisms.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>