Adds 5x50mm handgun.

A fairly uncommon machine pistol that loads 5x50mm flechette rounds and makes
a nice little sidearm for when something heavily armored and angry shows up
on your doorstep.

Spawn groups: military, pistols, allguns, homeguns.

Also boosts burst rate of flechette carbine to ten, as five is quite low
for a gun with such a large ammunition capacity.