Add compat_checkrunawayscript

[TDRRmk2]

Disables runaway script termination by default and puts it behind the compat_checkrunawayscript compat flag.

My reasoning is that this limit causes problems for mods that have to do a lot of work in ACS, mostly at map start. The CVAR should be a compat flag since at least in some Skulltag/Zandronum mods the limit is necessary, otherwise a script will keep looping forever and hang the game, and this is likely the case too for some ZDoom mods.
Keeping the option may also help users find infinite loops in their scripts if necessary, but without stopping everyone that would need it off.

[coelckers]

I don't think this is a good idea. If you need a script that runs for this long, better consider splitting it up