fix documentation and test of getoutput

it returns both stdout and stderr
closes gh-3280
allow test_process to succeed without python installed
Fix: "python ABS/PATH/TO/ipython.py" fails

The following line in setupbase.py was the problem.  It assumes
that your CWD is always at the repository root.  This patch removes
this assumption.

    execfile(pjoin('IPython','core','release.py'), globals())
fix callbacks as optional in js kernel.execute

plus some doc fixes.
Mainly to fix some backward compatibility with examples here and there.
Typo : optionnal -> optional
Add a CommandListDispatcher

This basically calls every registered hook and executes it, returning
a list of results.

Usefull as if more than one hook should act when a hook is called.
Add facility to register new hooks

new hooks can be defined by calling
`get_ipython().define_hook(name, dispatcher)`
Add a post_save_hook for notebooks

The replaces the "--script" functionality and can be used as an
notebook extention.
Replace the --script useage with the new hook mechanism

I real mechanism to register new hooks is still needed.