[#287] Add is_datastore_supported method to tests and engine_is_pg to model
[#287] Log warning if the database is not a pg database. Skip datastore tests, if there is no support for them.
Merge branch 'master' of github.com:okfn/ckan into 287-datastore-tests-only-on-pg
Merge branch '287-datastore-tests-only-on-pg'