Header guards according to convention.
Merge pull request #125 from murrekatt/include_guards

Header guards according to convention.
OTCachedKey: Replace tinythread mutex with std::mutex
OTLog: Replace tinythread mutex with std::mutex
OTSocket, OpenTransactions: Replace tinythread mutex with std::mutex
OTCrypto: Replace tinythread mutex with std::mutex
OTCachedKey: Replace tinythread with std::thread
OTCrypto: Replace tinythread with std::thread
Remove tinythread