I introduce a template method into the PTR_CAST machinery
to maintain constness.
There is now a FIXME in sd/../docshell.cxx because I needed
to use a dynamic_cast there to work around the games it appears
to be playing with OLE in-place activation.

Signed-off-by: Stephan Bergmann <sbergman@redhat.com>,
dropping the GCC-extension, unnecessary use of typeof from tools/rtti.hxx

Change-Id: Iba5ace1aa27e02b34fcc91af1e658c43371afd03