FLAG_ACTIVITY_NEW_TASK re-added to floating windows

ActivityStack modified to not cancel results if window is floating and "new".

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Aaron merged the original patch for testing -- however he also mentioned that removing FLAG_ACTIVITY_NEW_TASK causes some apps (G+?) to not quit halo when pressing outside of the window.  Should that be the case with the changes I made that were recently merged, _this_ should return the behavior back to what was originally intended as well as address the activity result cancellation issue the original patch was created to fix.