Remove dependency on Pyflakes.

Most of the pyflakes detection features now come for free within
pythran, so better avoid extra code.
Give tribute for a code snippet from codepy.

Most pieces of code from cxxgen.py are borrowed from Andreas Klöckner
work.
Improve optimizations documentation through docstrings.
Fix tuple noramlizations that was incompatible with OpenMP directives.
Code cleaning and reformatting.
(try to) Improve the user Manual

- split install section intro "prerequisite" and "installation"
- specify that gcc>=4.7 is required
Uses string.startswith('...') instead of a regexp

Aka the right tool for the right job :)
Remote redundant import
Defensive approach in the pass manager when apply() on unknown pass type

I still don't know if we should raise or warn or whatever here. At least
do not call blindly display() unless there is a super-class for passes
that provide it.
Defensive programmign apart, code is more readable with the check for
'Analysis' type. Still wonder if "transformation" is the right name
for the pass.
Improve comments in syntax module (Pythran Syntax Checker)

Conflicts:
	pythran/syntax.py
Merge pull request #37 from joker-eph/master

(Mostly) cosmetic changes
Take into account Pierrick's review.
WIP
Move slice in its own file
Fix bugs in handling of nested functions.

Met when a function includes a function that includes a function...
Draft version.
Attributs and Subscript access can be use for an object
Add tests cases from OpenACC example
Foreign code is now pep8 compatible
Few cosmetic modifications.