Conditionnal OpenMP validation

Disable OpenMP validation if OpenMP is not supported by the underlying
compiler (e.g. clang++)
Do not try to infer type from assigned slice/ext slice
Refactor pythran namespace naming

Funny bug: previous value once led to the namespace __pascal that was
used by clang...
Simplify Type inference

To the price of a small regression (see new skipped test), compilation
times are now reasonable with gcc.

The key is to *not* perform two typing passes but only one.
Full clang compatibility

After a few changes in the core::list code, pythonic is now compatible
with clang.

Most issues were related to implicit casts leading to ambiguous
conversions...

pythran/tests/cases/quicksort.py led to the return of uninitialized
value,but their is already an issue opened for this case.
import extended slices performances
Update TODO list
Enable definition of function with the same name than an intrinsic
Fix len for tuple

* std::tuple doesn't have ::iterator type attributs
Fix zip if all operator doesn't have the same size
In operator for sliced_string in string
Improve string interface

* split, startswith and endswith
Add file type information
Fix imap != operator
pythran should be usable from dev folder

* workflow will be really slower if we need to reinstall everything before each little test. Pythran should have +x right
* Exception have to be exported if we want to catch it
Change std::array to core::array to support conversion constructor

* for : a = ((1,2),(2.5,3.5))
Make tuple use std::make_tuple for real tuple