CMDHELPER-2624 - Reported by jb_aero

1. Compiler should be run on a separate thread.

2) Change default aliases file to something with the .msa extension - DONE

I'll add to this that it's starting to get to the point where the compiled files should also be serialized and output to the file system. Even something dead simple would be an improvement, with good change detection. Even if the system does a clean build at startup, it would be an improvement during development for it to only recompile changed files.