Make gunsling pocket available only if you have gunsling attached

[steph-pg]

Allow to use gunsling pocket only with weapon that has rifle sling attached. It's more realistic than to have a heavy mg without a sling to being somehow magically attached to merc's body.
You would need to carry a shovel, machete and crowbar somewhere else

[kitty624]

This should be accompanied by a gamedir change adding rifle sling as attachment to all desired weapons, i.e. including launchers like m79 or milkor and other two handed weapons that reasonable could have a rifle sling

[majcosta]

I like, but like kitty said there's stuff that needs to happen before this can be merged. Make sure everything that you'd like to fit the sling slot CAN take a sling attachment. you'd probably need to make dropping items from hand(s) cost 0 AP not to turn this into endless frustration too.