Reimplement OS/2 PM window support to separate the drawing operations

Reimplement OS/2 PM window support to separate the drawing operations
from the windows.  All drawing operations now operate on objects that
represent "presentation spaces"; a window has a PS associated with it,
but it is now possible to create other PS objects that represent
bitmaps.  Furthermore there are is a bitblt operation that can be used
to move image data between bitmaps and windows.  All of this support
allows Scheme to store its graphics output in bitmaps and to refresh
the windows when needed, thus allowing efficient backing store for
windows.