Multi-Admin Backport

Does exactly what it says: allows more than one admin to be active at a time. Comes with a few changes as a result:

• verify has been renamed to promote
• A new command called demote has been added, which can be used to remove admin privileges
• The admin global variable in Lua now points to the first entry in the adminplayers array for backwards compatibility reasons.
• IsPlayerAdmin() has been exposed to Lua. In the future, this function should be used for any and all admin checking in Lua.

I made a few mistakes during the backport (since this junk is over a year old) so a review would be appreciated. I think I fixed everything, but I wouldn't be surprised if something slipped past me.