WARNING!!! This is an important change.

This is the continuation of the effort to structure libCore into
independent sub-packages.

A new class TDirectoryFile is introduced. It derives from TDirectory
and takes from TDirectory all the I/O functions.

All the classes (except TROOT) deriving from TDirectory are now derived
from TDirectoryFile. TDirectory keeps the previous API for back compatibility
with several functions made virtual.

This change should be back compatible, except if the user codes creates
a file sub-directory by direct invokation of the TDirectory constructor
instead of calling TDirectory::mkdir.

Note that TMapFile is not yet fully adapted to the new scheme.


git-svn-id: http://root.cern.ch/svn/root/trunk@17419 27541ba8-7e3a-0410-8455-c3a389f83636