scheduler: switch from boost to std

Changes from boost::chrono to std::chrono, boost::condition_var to
std::condition_var, boost::mutex to sync.h Mutex, and reverselock.h to
sync.h REVERSE_LOCK. Also adds threadsafety annotations to CScheduler
members.

test/lint/lint-includes.sh

@@ -53,7 +53,6 @@ EXPECTED_BOOST_INCLUDES=(
     boost/algorithm/string/classification.hpp
     boost/algorithm/string/replace.hpp
     boost/algorithm/string/split.hpp
-    boost/chrono/chrono.hpp
     boost/date_time/posix_time/posix_time.hpp
     boost/filesystem.hpp
     boost/filesystem/fstream.hpp