cubicweb #2715115 rewrite uses of the cmp function [validation pending]

Python 3k does not have a __cmp__ function for details see: http://docs.python.org/3.0/whatsnew/3.0.html#ordering-comparisons

prioritynormal
typeenhancement
done in3.17.0
load1.000
load left0.000
closed by#80783605d270 [toward-py3k] rewrite __cmp__ (closes #2715115)
patch[toward-py3k] rewrite __cmp__ (closes #2715115) [applied]