Correct handling of the -e switch

A regression led to the generation of BOOST_PYTHON code with this flag,
which is incorrect. Improve dic/CLI.rst to document the interface and
add a few extra test cases to prevent such regressions.

Add pythran-config script similar to python-config to help third party
compilation.
Add proper error logging for an unlikely situation

The test suite did not capture the situation when an exception was
raised in Python and not in Pythran.
Fix pythran long header when GMP is not used
Add missing headers

The problem only arises when the headers are included directly from C++.
There is currently no test case for this situation, as it is not the
most useful part of Pythran, still writing a pure C++ test suite for
Pythonic would be a great way to deal with this kind of issue!
Add basic SIMD testing

This is *not* to have full coverage, but rather to prevent regression
from what is already supported, as no testing is done otherwise. As a
consequence, some tests are commented in test_simd.py.

Note that this forces the inclusion of a large part of Boost.SIMD, and
thus the tests are running slower, (but only if boost.simd is activated
and numpy is used)