Fixes to support ActionBarSherlock.

AlertDialog.show() and Dialog.show() now temporarily pause the UI thread.
Libraries that don't have an AndroidManifest.xml now default to "org.roboletric.default" for package name.
Centralized ApplicationInfo and PackageInfo creation.
Implemented AssetManager.openXmlResourceParser().
More hacks to get ViewRootImpl into the right state.
RoboWindow.getDecorView() runs with looper paused.
Fix bug in ShadowHandler.sendMessageAtTime().
Remove commented-out code.
Capture calls to System.nanoTime() so things are more deterministic.

Reverts 14ec805515e078bf0019c34a55386da142f686fc in favor of using the main Scheduler's time.
Remove ShadowMessage.