Code review comment for lp://qastaging/~edwin-grubbs/launchpad/bug-433809-picker-search-slash

Summary
-------

This bug fixes the problem where adding a slash to the search for
a project series always yields zero results.

Since I converted ProductSeriesVocabulary.search() to use storm
directly instead of the sqlobject compatibility layer, I updated
the getTermByToken() method to also use storm.

This will be landed on devel, but since devel still hasn't had
db-devel's changes for 3.1.11 merged in, I'm targeting this
merge proposal to db-devel so that the automatic diff will be correct.

Tests
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./bin/test -vv lp.registry.tests.test_productseries_vocabularies

Demo and Q/A
------------

* Open https://launchpad.dev/ubuntu/hoary/+source/alsa-utils/+edit-packaging
  * Click the "Choose..." link.
  * Searching for "fire/" should show two matching series.
  * Searching for "fire/t" should just show 'firefox trunk'.