[mojosetup] Expose the runScript interface to allow non LUA scripts to be run

[Ryan C. Gordon]

>> Any objection to me changing this to a Lua boolean type?
> 
> None at all.

Okay, next time you sync up, please change any existing calls to this in 
your existing installers. If they passed 0 for /dev/null, this will 
translate to true, which isn't what you want; Lua treats false and nil 
as boolean false, and everything else--including zero--as true. You have 
been warned!.

--ryan.