#373 use ignore_missing instead of ignore
[#2750] Update test_example_idatasetform_plugin.py for CKAN 2.0

Not the best or most thorough test case ever but it's something, and it
passes.
Merge branch 'master' of github.com:okfn/ckan into 2750-add-docs-and-examples-for-idatasetform-and-igroupform
Merge remote-tracking branch 'origin/2750-add-docs-and-examples-for-idatasetform-and-igroupform' into 2750-add-docs-and-examples-for-idatasetform-and-igroupform