Fix a memory leak in browser tests.

Don't load suites with excluded tags.

prep for release (dart-lang#754)

Platform selectors for operating systems now work for Node.js tests.

Add support for node_modules

Add pumpEventQueue() and neverCalled.

Increase the timeout when loading tests.

addTearDown() now adds to addTearDownAll() in setUpAll().

Fix test hang and prep for release - 0.12.26 1 (dart-lang#715)