Because some stuff wants to multiple-inherit from VclAbstractDialog and
OutputDevice-subclasses, and we'd prefer to keep all the lifetime
management through a single smart pointer class (VclPtr)

The change in msgbox.cxx and window.cxx is to workaround a bug in
VS2013 to do with virtual inheritance and delegating constructors.

Change-Id: I178e8983b7d20a7d2790aa283be838dca5d14773
Reviewed-on: https://gerrit.libreoffice.org/29140Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Noel Grandin <noel.grandin@collabora.co.uk>