Fixes for intermittently broken tests (custom assertion bug and sinon.js bug workaround).

Rewrote custom assertion to eliminate timing issue that caused intermittent invalid test failures.
Added test/build.xml and test/build.properties.

Executes the Mocha unit test suite using Karma Test Runner against all supported Sencha Touch and Ext JS versions for the set of browsers specified in build.properties.
Added 'test' target to root build.xml.