remove key restriction in test.

At this point in the test, there should only be one `Thread` object.
However, because of previous tests, MySQL does not necessarily give
that object id=1. By not specifying the id, the test does the intended
thing. The get() function will fail if more than one object matches,
so the test will still barf if more than one Thread object exists.
Merge pull request #131 from bobbydavid/mysql

remove key restriction in test.