GDI+ wrapper: add handling for EXIF Orientation flags

This was mostly a curiosity, since I now have code available for both
reading JPEG metadata and easily rotating images via GDI+.  Seems to
work well, though I don't have test images available for all
orientations.  (The cardinal directions without flipping work properly,
as tested on some iPhone photos, but I don't have any images from a
flipped sensor.)