We can avoid setting a default value for epoch since we intend to mean
unset and "0" as the same thing. This is also a more consistent default
as the display of epoch=0 is no epoch at all in the full package
version.
The extra paranoia in get_full_version can be removed due to lint_epoch
guarding against non-integer values of epoch.
Signed-off-by: Allan McRae <allan@archlinux.org>