Avoid silent failure when reaching the maximum amount of TRef.  When a
TProcessID is full (has seen 16777215 objects), we switch to new one TProcessID
(maximum 65535 including the TProcessIDs read from file).  TRefArray can not
switch to new TProcessID if they already contain objects.

Some of the new warning/errors:

Warning in <TRefArray::AddAtAndExpand>: The ProcessID for the 0x5f83819e8 has been switched to ProcessID4/6c89f37e-8259-11e2-9717-166ee183beef:4

Error in <TRefArray::AddAtAndExpand>: The object at %p can not be registered in the process the TRefArray points to (pid = ProcessID4/6c89f37e-8259-11e2-9717-166ee183beef) because the ProcessID has too many objects and the TRefArray already contains other objecs.


Warning in <TProcessID::AddProcessID>: Maximum number of TProcessID (65535) is almost reached (one left).  TRef will stop being functional when the limit is reached.
....
Fatal in <TProcessID::AddProcessID>: Maximum number of TProcessID (65535) has been reached.  TRef are not longer functional.


git-svn-id: https://root.cern.ch/svn/root/branches/v5-34-00-patches@48797 27541ba8-7e3a-0410-8455-c3a389f83636