Slight jsexecute.js improvements

[zanxz-lol]

I made super small improvements to listIndex(), and listIndexSlow().

listIndex() no longer expects a string index first because numbers are more usually passed than 'last', or anything similar.
listIndexSlow() is more concise.

Also, checking with indexOf() first in listContains() is faster than only using compareEqual(). I was clearly on something last night..

[GarboMuffin]

It helps if you can show at least some micro benchmark where these are faster

[zanxz-lol]

listIndex() test done with no warp timer, tested 100,000 times each for 'any', 'last', and normal numbers:

numbers-old.txt
old average: 0.0001550000002483527 seconds

numbers-new.txt
new average: 0.00015333333303531012 seconds

Do you also want listContains() tests?

[GarboMuffin]

I don't need to see listContains

Can you provide the script you're using to benchmark listIndex?

The difference is small enough that you can't draw any conclusions from it