Properly avoid repeated calls to TStreamerInfo::Build*
Properly avoid repeated calls to TStreamerInfo::Build*

-Internal cloning of TStreamerInfo resets kBuildOldUsed so BuildOld will run
-BuildOld calls itself recursively so we only set kBuildOldUsed once we
 leave the function
-Avoid repeated calls to Build
These changes are needed to avoid having multiple threads do the same
work on the same TStreamerInfos which can cause interference between threads.

Dr15Jones/root,Dr15Jones/root,Dr15Jones/root,Dr15Jones/root,Dr15Jones/root,Dr15Jones/root,Dr15Jones/root