[#1612] Treat zero as infinity for facets

For historical reasons, limit=0 needs to be treated as infinity.
[#1878] make (org|group)_member_create return dictized membership

Conflicts:
	ckan/new_tests/logic/action/test_create.py
[#1873] setup template variables at start of member_new controller

If a validation error was thrown, then the template would be rendered
before these variables had been setup.
Refactor datastore unit tests

For some reason, on the 2.2.1 branch importing datastore.plugin causes
failures on unrelated datasets because the datastore plugin is not
properly loaded. It seems to be caused by circular imports but it's too
hard to find the cause.
[#1465] exclude more unlikely cominations
Merge branch 'fix-2.2.1-tests' into release-v2.2.1