Permit tags in script constants

This was previously allowed sometimes by accident (if statement double
parsing, which was fixed in a recent commit)... it's a useful enough
feature that it should stay, despite originally being a bug.
Also, fix meta typo.
Add new ACTION command, to match EVENT

A command to run NPC actions! Full meta, mostly!
Also patch an event command bug.
Also patch some meta.
Merge pull request #755 from mcmonkey4eva/master

Pull request for requested fixes