Really make reco::TrackBase destructor virtual

Back in January 2008, an attempt was made to add a virtual destructor to reco::TrackBase and its derived classes, such as reco::Track.  Unfortunately, the virtual keyword was not added in TrackBase, just a comment stating (incorrectly) that the destructor was virtual.  This is a bug, as the class needs a virtual destructor.
This request merely adds the virtual keyword to the destructor to fix the bug.  It was tested with checkdeps -a, and the unit tests pass.

This is a trivial C++ bug fix that has nothing really to do with RECO, so if it is not signed in a timely manner, I suggest that the signature be bypassed.

The bug causes a unit test failure in CommonTools/Utils when the Reflex functionality for invoking functions is replaced by ROOT.  So, this fix is needed.