center on alien melee/psi attacks
don't center on dead units

previous commit took care of the case where it was relevent
smooth scrollin' bullet cam

not gonna put this in the options menus, since it's getting overhauled,
and that's just gonna create more work. not gonna add strings for it either
because i'm not sure what the implementation will be.

for the time being, to see this feature in action you will need to add the
following line to your options file:

battleSmoothCamera: true