Make caching of fProperty and fInterShowMembers thread safe

The setting of the caches held by fProperty and fInterShowMembers
can happen on different threads. Therefore the values themselves
are now atomic and appropriate locks are held when updating the values.
Take lock before calling cint

Must serialize access when getting type related information from
cint.
Added additional error reporting

While debugging a problem related to thread safety these additional
checks and error reports were very helpful.
Merge pull request #34 from Dr15Jones/additionalThreadSafetyFixes_v5-34-21

Additional thread safety fixes v5_34_21