changefileheader2: #i109125#: change source file copyright notice from Sun Microsystems to Oracle; remove CVS style keywords (RCSfile, Revision)

 Apple g++ 4.0.1 erroneously believes that it is ambiguous to use
 WeakReference<XInterface>::operator=(Reference<XInterface>).
 as a workaround, introduce WeakReferenceHelper::clear(), and fix all users.

 avoid creating a temporary WeakReferenceHelper for uno::Reference assignment.
 [according to callgrind this is 3 times faster]