This prevents needless calls to db_connect() if we already have a
reference to a handle we can pass into a function. Although the current
underlying implementation using mysql_connect() will return the same
connection if all parameters are the same, this might not be true if we
switch to a more modern (e.g. PDO) interface.

In the face of safe transactions, it is extremely important all actions
are being taken over the same connection to the database.

Signed-off-by: Dan McGee <dan@archlinux.org>
Signed-off-by: Lukas Fleischer <archlinux@cryptocrack.de>