the static TRef::SetObject() works on TRef::fgObject, and is a misnomer
wrt TRef::GetObject(), which works on the referenced object. This patch
names the access to the referenced object GetObject(), while the access
to the static fgObject will be called Get/SetStaticObject(), where
GetStaticObject() is a new function.

TRef::SetObject is kept (for the time being) for back compatibility.

I did not implement TRef::SetObject(const TObject*) (as an alias to
operator=(const TObject*)) to ensure that this interface change will
result in a compiler error if the old TRef::SetObject (now
TRef::SetStaticObject) is used.

Also, TRef::GetObject() now sets fgObject to "this" before calling the
TExec, allowing the TExec to access the TRef's fUniqueID, so it can
determine which object needs to be dereferenced. I need this for storing
the documentation objects.

Docs and the tutorial GetWebHistogram are updated accordingly.


git-svn-id: http://root.cern.ch/svn/root/trunk@12543 27541ba8-7e3a-0410-8455-c3a389f83636