trac 172XX : cleanup of pep8 E222 and W601 and raise in src/sage/combinat
Trac #17270: cleanup of several minor points in sage/combinat

This aims to clean up three things:

* deprecated use of raise
* deprecated use of has_key
* pep8 error E222

in the combinat part of sage only

See https://groups.google.com/forum/#!topic/sage-combinat-devel/f7SE-
5BpRZg

URL: http://trac.sagemath.org/17270
Reported by: chapoton
Ticket author(s): Frédéric Chapoton
Reviewer(s): Nathann Cohen