SQL: Added two indices
SQL: Added two indices

This brings the average page generation time for VN pages down from
~170ms to ~90ms (when measured over a period of a few hours).

I haven't put this in an update script, if you want to take advantage of
these indices make sure to manually add them yourself.

erengy/vndb,morkt/vndb,christian-roggia/vndb,morkt/vndb,christian-roggia/vndb,erengy/vndb,erengy/vndb,morkt/vndb,morkt/vndb,christian-roggia/vndb,morkt/vndb