New import/export framework

[Leonard Rosenthol]

> Import a Gimp image with two layers works a bit: two layers are
> created. We don't read the right transparency, though. If this is not
fixable by
> extending the ImageMagick reader,
>
	The IM .xcf import module is certainly not complete - I wrote enough of it
to support some work that I was doing at the time.  I don't believe that
anyone has picked it up and done anything more with it (except for the
occasional bug fix).  So PLEASE - feel free to do so!


Leonard