M42A can have Burstfire enabled

[jaggaaff]

Bug Description:
Apparently the M42A when it's fresh out of the box can have burst-fire enabled which shoots two rounds in one click, and appears to not suffer accuracy or recoil penalties.
It can also attach a burstfire field modification but if you remove it, It removes the burstfire ability. If you reattach it, you can burstfire again.

Steps to reproduce:
1.Be a specialist(or spawn in the M42A)
2.Enable it's burstfire
3.???
4.Profit while xenos rage by getting two shotted by a .50 caliber sniper.

[forwardslashN]

This is a good catch. I fixed both.