Reactivate -p flag that was not forwarded anymore
A few code cleaning

Nothing that really matters:
- some more perfect forwarding
- more type inference combination
- an uninitialized variable
Improve performance of numpy's ndarray indexer

* Use a specialization to correctly handle the 1-dim case
* Avoid to create the underlying object over and over
* Fix behavior when using constant indices
Support optional parameter for exported functions

given a function like:

    def foo(a, b=0):
        ...

it is now possible to export it as

    #pythran export foo(int)

and

    #pythran export(int, int)