Print warning if ACS script from one mod overrides another

[StroggVorbis]

Right now, GZDoom only prints a warning/error to the console if a script number is defined more than once in the same behavior lump, but not if two mods with same script numbers or names are loaded one after the other, even if developer is set to 2.
This makes mods harder to debug which happen to share the same script number, as the user isn't informed if one script has been overriden and the mod now exhibiting different/broken behavior as a result.

Example would be loading Xaser's Parkour after Tekish's SimpleUIaddons. The latter overrides the former's script 891 and 892, breaking Synthfire and causing the chaingun to get stuck in the fire state. A casual look at the console would show no issues present.

[Lord Misfit]

Though this isn't a bad idea by any means, one response to this [and a valid enough one] will probably be along the lines of "using named scripts is more likely to avoid this problem", but at the same time really old mods didn't have the luxury of named ACS scripts either. That and that advice is more useful to an active modder than for a mod that's discontinued.

Again, I don't mind this, though I would add the request for having this check named scripts as well as numbered ones.