[Bro-Dev] script loading implementation

[Jonathan Siwek]

> I'm not sure I fully remember how the @load mechanism currently
> tracks what's loaded,

It looks like it tracks whatever string is given as an argument to @load (or as an arg to bro), and if it ends in .bro, it also tracks the version with that stripped.

> but could it just generally canonicalize all scripts
> to their full *absolute* paths of the actual files being loaded
> (i.e., always including the .bro extensions) and then remember those?

Yes, I think that works best/easiest.  I can work on this.

- Jon