Fix bugs in autocomplete tests that prevented the suite from loading.
Fix bugs in autocomplete tests that prevented the suite from loading.

Fixes #2061

Author: glyph

Reviewer: exarkun

This also corrects a bug which prevented a ''valid'' object from within the test module preventing it from loading, and adds a test for the is-this-a-test predicate that we use so that other non-test-class objects may be defined in JS test modules.

twisted/mantissa,twisted/mantissa,twisted/mantissa