Allow key binding specific skills by name

[argv-minus-one]

I just noticed that one can use any skill, with no EP cost and without having actually learned it, by pukenameing its script—even if cheats are disabled (e.g. on Hell or Armageddon difficulty). Appropriate checks should probably be done at the beginning of those scripts.

This could actually be useful, by the way. This would let the player bind a key to a specific skill, rather than to a skill ring slot, allowing for more than eight skills to have key bindings and freeing up skill ring slots. At the moment, though, doing so would be cheating, and that's no fun.