it used to create image% objects that were simple containers for the
data in the file; the change _should_ be backwards compatibile;
the only know incompatibility is that the get-filename method
now returns a path instead of bytes (this is to match the
image-snip% class)
closes PR 1168
please merge to the 5.1 release branch
including adding some uses of `with-module-read-parameterization'
so that `read-accept-lang' is set right anyway; still, so many
many places just set `read-accept-reader' to #t that making
`read-accept-lang' #f by default looks like too big of an
incompatibility
