New flags for hitscan and rail attacks

[Ichor]

Since the projectile cross/hit bug won't be changed (no complaints about that), I have devised a workaround. That is to use -ACTIVATEPCROSS on all projectiles (or at least, all important ones). That works perfectly, with rockets or hammers flying over the trigger line without problems, but will still trigger on impact. No problems here, and I don't intend to use projectile cross triggers anyway. However, that does not work for hitscan or rail attacks. So unless there's some way of doing the same thing already, perhaps a couple of new flags like FBF_NOSHOOTACTIVATE and FBF_NOCROSSACTIVATE could be added that could disallow hitscans from triggering linedefs upon impact or crossing. This could also be used to prevent, say, a sniper dot from accidentally pressing a shooting button, or breaking a glass window and awakening whatever nasty thing is behind it, or maybe destroying a crate (using a Floor_LowerInstant script) that you were going to use as a platform later on.