Workaround for ROOT 6 problem with forward declarations

This is a workaround for a ROOT 6 problem.  This workaround was requested by Danilo Piparo.
Danilo's explanation follows:
One of the ingredients needed to enable delayed  payload parsing is the forward declaration of classes, functions and typedefs. ROOT automatically produces them, transparently for the user.
I found a case in CMS where this "automatic forward declaration" does not work.
It is in the TrackingTools/PatternTools package and I worked it around adding an entry to the selection file (src/classes_sel.xml):
<class name="GlobalErrorBase<double,ErrorMatrixTag>" />
[More detail omitted for brevity]
Now, I [Danilo] am *sure* I can debug this with some time at disposal, say one morning, but unfortunately tomorrow I will leave for a 2 weeks vacation.
I proposed to add the selection because it will make the cms jobs succeed and is relatively cheap to add.

Please merge this as soon as convenient.