[test] Gather tests about mail module From sobjects/test/unittest_notification.py to test/unittest_mail.py where other tests for mail.py are already. Some style fixes along the way.

[web/component] guard against invalid page_size form parameter Same as dff28956f37e, except the almost same code exists in two places (yay us).

[predicates] fix paginated_rset for components that change page_size_property The predicate and component had better agree on the page size.

[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.