potion-0.1.1061 release

jit: fix getlocal,setlocal jumps with lots regs overflow

with >15 locals the previously added getlocal,setlocal jumps had the wrong target
and therefore the offset calc. was wrong.
add more jit docs.
nbody n=50000 works now.

cherry-pick p2 from here

_why's version as of his disappearance, plus a few minor bug fixes