Internal fixes for async timing and truthy tests.

• Unbinding temporary computes now uses (polyfilled) setImmediate instead of a 10ms timeout. This is to make dependent events happen in queue more consistently with mutation observer events (which also use setImmediate in vdom, and native immediate timeouts with real DOM).
• COMPUTE.truthy now doesn't automatically evaluate functions if computes return them as values. This supports using "@" expressions (which do not evaluate a reference function to its returned value) with {{#if}} in can-stache.
• Some external dev dependencies updated: testee and generator-donejs