Stug & StuH MGs continue firing if hold down fire while moving to ineligible firing position

[Matt Hands]

If you hold down the fire button while buttoning or unbuttoning (to an position where you can no longer fire the MG), the MG continues to fire until you release the fire button.

[Matt Hands]

I have a fix and will commit in due course. Just working my way through a backlog of tangled commits !

Today I am moving all vehicle MGs to extend DH_ROMountedTankMG, so can put generic fixes in one abstract parent, without need for lots of subclass overrides.

[Matt Hands]

Fixed in commit 01edf8a.

[Matt Hands]

Extended to cover single player mode in commit a0722c8.