Provisional WMF/EMF support

At the request of GioRock, I've added provisional WMF/EMF support to PD.
By provisional, I mean that WMF/EMF do not appear as items in PD's
common dialog boxes, but if you drag/drop a WMF/EMF file (or load it via
All Files in the CD), PD *should* now load it without trouble.

Some GDI+ oddities still occur.  For example, on some images, it reports
much larger image sizes than MS Paint, for reasons I can't easily
ascertain.  I'll investigate when I have time.

One neat feature I've added is a conversion to EMF+ format when
possible.  This means that WMF/EMF files will render much better than
(any?) competing software, with full support for alpha, antialiasing,
and more - which actually makes WMF/EMF usable!