Fix completion percentage calculation in mirror status

We sometimes record a duration even on a failed fetch attempt, such as
if we get an HTTP 404. However, we never record a last_sync value on a
failed fetch. Use this field instead to sum up the total number of
successful checks.

Signed-off-by: Dan McGee <dan@archlinux.org>
Bump South requirements.txt version

Signed-off-by: Dan McGee <dan@archlinux.org>
Bump to latest Django security release

Signed-off-by: Dan McGee <dan@archlinux.org>
Bump jsmin requirements version

Signed-off-by: Dan McGee <dan@archlinux.org>
Proper support for revoked signatures

The 'valid' column wasn't quite right. Add a new 'revoked' column that
works similar to the one we have on keys and use it instead, properly
parsing the output from `gpg` signature data and looking for the magic
prefix string.

Signed-off-by: Dan McGee <dan@archlinux.org>
Bump requirements