When USER_LIMIT == 0 (no limit) $UserCount is always > USER_LIMIT so
the notice is always shown. Actually this commit just implements the
exact opposite of the logic on line 137.

Source field insertion makes every infohash different so this doesn't do
anything

Untested partial fix for issue #36

- Check post size
- Use prepared queries
- Remove now-pointless injection protection

Tenboro said to

This includes complying with standards that allow mobile browsers to
create a pseudo-app out of the site, complete with homescreen icon,
splash-screen, and a minimal browser-less UI