Re-enable testsuite for numpy

* relative path for test cases that opened file where wrong
* every numpy test cases raised an exception and were not run
* some runas entries had syntax errors

The reason behind this was that exception raised during testing were a
bit too eagerly trapped and not raised...
Fix extended slice with implicit dimension
Fix dangling ref in ndarray implementations

For performance reason, it is important to take a ref of the array when
creating a view. However this can end up with dangling references, so
use reference qualifier to distinguish between the two.
Fix result type extraction

One has to remove the const qualifier of the return type to match the
specialization of ``pythran_to_python``
Fix bad implementation of str.strip

Empty string was badly handled
Fix rangeextract test case

There is no pythran converter for generators, so expand the generator to
return a list instead.
Fix bad operator-- for nditerator

What a shame...
Update range tests cases parameters

Testing random routines is always painful :-/