Fix a few typeahead issues.

typeahead.js caches its Datasets by name, so typeaheads sharing names
forced them to share dataset options, which made add a tree continue to
show the list on focus.

We also were missing the trailing '/' on URLs, which was causing two
requests, one for a 301 redirect.
Merge pull request #771 from maurizi/fixTypeaheads

Fixes a few typeahead issues.