Fixing failfast for single threaded benchmarking
Add test coverage analyse

Based on pytest_coverage.
Pythran currently has a pretty decent 90% coverage rate!
Fix a few compilation warnings
Make all tests use -Wall

The goal is to detect warnings in pythonic, *but*
this is not perfect as it also detects warnings in the generated code,
and test cases are full of warnings, although this commit fixes quite a
lot of them.

This only affects test cases based on TestEnv.
Harmonize integer template parameter types

Sometimes int was used, sometimes long, sometimes unsigned long.
Now size_t is used *everywhere*