Thread safety fixes for TCint

-use thread_local for statics which are being used as return values
-use C++11 initializers to allow static containers to be const
-add lock to protect fgSetOfSpecials
Make function static return values thread_safe

Funciton level statics which are being used as return values from
the function are changed to thread_local. This is needed to avoid
multiple threads changing the values while they are being used.
Added missing locks when calling gCint

Added calls to the gCINTMutex lock when calling gCint methods. These
are needed to avoid problems while concurrently using TFormula.
Make TClass::fIsAMethod setting thread safe

Caching and initialization of TClass::fIsAMethod have been changed
to make them thread safe and for calls to the TMethodCall can happen
concurrently.
Merge pull request #26 from Dr15Jones/anotherFixForTFormula_5_34_21

Another thread safety fix for TFormula
Merge pull request #28 from Dr15Jones/threadSafeTClassfIsAMethod_cms-5-34-21

Make TClass::fIsAMethod setting thread safe