[devtools] fix get_bounds Say an attribute has two IntervalBoundConstraints, one with minvalue=0 and the other with maxvalue=10 (not literally, or that could be a single constraint, but e.g. with references to other attributes). We don't want to override the minvalue of the former with None just because the latter happens last in the constraints list. This doesn't fix the case where two constraints both have a min or a max value. Meh.

[devtools] "fix" boundary condition for autofill maxvalue in an IntervalBoundConstraint is inclusive. If the min and max values happened to coincide, we would call random.choice on an empty list, which it didn't like. This is still broken in the case of BoundaryConstraint('>', minvalue), as we assume the minvalue is in the range, but that's something for another time.

[test] Use stdlib doctest module instead of logilab-common class The former just works fine now but the later does not play well with py.test.

[test] Re-implement generative tests with subtests