Rename fReadingBasket to fReadingObject in TROOT.h

Rename TROOT::ReadingBasket to TROOT::ReadingObject
Rename TROOT::SetReadingBasket to TROOT::SetReadingObject
TROOT::SetReadingObject is now set in TKey::ReadObj
One can test in the default constructors (like TCanvas) if Root is
reading from file or socket.
The TCanvas default constructor has been modified to take advantage
of this change. As a result, the following works:
 root > TCanvas c1


git-svn-id: http://root.cern.ch/svn/root/trunk@623 27541ba8-7e3a-0410-8455-c3a389f83636