Adds flintlock carbine.

This thing exists stats-wise somewhere between the flintlock pistol and
the flintlock rifle.
Spawns in museums, mansions, and rarely in pawnshops, the same places as
the current flintlocks. Includes recipe and 'no old guns' mod support.
Merge pull request #9702 from Rivet-the-Zombie/flintlock-carbine

Adds flintlock carbine.