Increased the distance of the FLF ships that attack you in es00.

Well, actually, I made them actually *have* a distance. vec2.add
with pairs of coordinates is broken; trying to use that method just
does nothing. At any rate, I increased the *intended* distance.
Those FLF ships being so close makes getting out impossible without
a highly *armored* ship; not a fast ship, but a highly armored ship.
This is completely nonsensical. The ships spawning a ways away makes
escaping from them with a fast ship much more realistic.

That bug with vec2.add still needs to be fixed, though. For now, I
worked around it by creating a new vector and adding them together
instead.
* Fixed the vec2 add/sub/mod/div to work as intended (modify object with :add(), not with +, etc...)
* Added some auto tests for the lua (vec2 only atm).
Merge branch 'es00_distance' of https://github.com/onpon4/naev into tmp
* Can simplify expression now that the vec2 stuff actually works.