Renames ThreadStartSempahore to Notificaton (by Vlad Losev);  adds threading tests for SCOPED_TRACE() (by Vlad Losev);  replaces native pthread calls with gtest's threading constructs (by Vlad Losev);  fixes flakiness in CountedDestructor (by Vlad Losev);  minor MSVC 7.1 clean-up (by Zhanyong Wan).