Bindings improvements + autogen behavior

 * This enables to have a local installation tree of nlopt bindings by stripping the octave/guile prefixes and replacing it by the real installation I provided instead of the system dirs, like what it is done whith the python bindings.
Of course, if prefix=/usr, nothing changes and it still will be well packaged.

 * Python3 compatibility
I had to use the numpy.i from numpy's dev trunk
I added an example script in /test compatible with both python2/python3.

 * bootstrap script: this script 'just' bootstraps, no configure step, the autogen script has the same effect as before but it calls bootstrap