Made const functions of AssociationVector thread safe

The AssociationVector uses a cache, transientVector_. The management of that cache is now thread safe if multiple threads call const functions simultaneously.
Fixed problems found when built with full release

-switched to the standard CPP defines used to hide C++11 constructs from ROOT
-fixed a typo in one of the constructors
-worked around an apparent gcc bug which did not allow me to specify a memory order
 for the compare_exchange_strong atomic method.
fixed_ is no longer a member of AssociationVector

fixed_ was declared a transient data member of AssociationVector.
However, fixed_ has been removed and if we do not remove it from
the Reflex transient storage declaration the Reflex parser dies.
Merge pull request #1268 from Dr15Jones/threadSafeDataFormatsCommonProducts

Multithreading fixes -- Made const functions of AssociationVector thread safe