Allow memstore instances to be started empty

This allows easier debugging of web UI problem.
Add test and make it pass
fix and iterator, add some logging, and reenable
fix the test, remove -short from .travis.yml
Merge pull request #116 from barakmich/issue114

Fix Issue 114 -- And subiterators may move forward on Contains, even if the And ultimately doesn't
Merge pull request #109 from kortschak/empty

Allow memstore instances to be started empty