Removed Schwarz counter that should no longer be necessary.

The Schwarz counter in vtkTimeStamp is no longer needed. Now
the atomic integer classes don't manage any pointers unless
native atomic classes don't exist. In that case, I added a check
for NULL pointers which should handle the case where the global
counter is deleted at exit time.

Change-Id: I038b27fc7fcd43d4c7024108f6ff3808e97b2b3f
Fixed information key initialization to be thread safe.

A long time ago, I had introduced a change to the way information
keys are initialized to address an issue on OS X 10.3. Since we
no longer support OS X 10.3 and we want key initialization to be
thread safe, I reverted that change.

Change-Id: Iaf7956a72c63957b9812569cf7eb092624b12999
Merge topic 'remove-schwarz-counter' into master

47ca0348 Removed Schwarz counter that should no longer be necessary.
Merge topic 'thread-safe-infokeys' into master

948bd014 Fixed information key initialization to be thread safe.