Default for JIT compiler: enabled or disabled?

[Rik]

6/30/13

All,

The default for the experimental JIT compiler is enabled whenever Octave
has been built with support for it.  I know Matlab has their JIT compiler
enabled by default, but theirs is not a new thing and has been extensively
tested.

I think it would be more prudent for Octave to disable JIT by default and
have any interested users specifically enable it and experiment with it. 
Eventually we can switch things around if warranted.  Any thoughts?

I would add a new command line option '--jit-compiler' to enable JIT from
the start of Octave since it would now be disabled to begin with.

--Rik