Change return fire behaviour

[Safety0ff]

The way current return fire works (correct me if I'm wrong):
If the droid receives damage, then simply reset state to "fire at will."

I think it would be better if the droids in "return fire" mode would only fire on droids and structures within range / guard area that are firing at objects belonging to their team/alliance.

Thoughts, comments?

[Safety0ff]

Here's a hack/patch to improve return fire behaviour:
http://pastebin.ca/1734674

Notice that you can now drive your troops into a base and they won't fire at things that don't shoot back!

Note that, like units set to hold fire, units set to hold fire might get stuck from behind simple enemy wall structures. That probably should be fixed in path finding.