the docs for gnome_vfs_async_xfer are somewhat fuzzy, I'll try to explain the
issues:

1) GnomeVFSAsyncXferProgressCallback is not linked (from the html docs), I
looked it up in the gnome-vfs-async-ops.h file. In that file it sais the
callback should always return 0, except if status is GnomeVFSXferErrorAction or
GnomeVFSOverwriteAction.

2) GnomeVFSXferProgressCallback is in the html docs, but without description

3) both callbacks return gint, it seems unlogical that both have to pass the
user descision to gnome_vfs, so what should the return value be for both of the
functions?

4) returning 0 by default (as written in gnome-vfs-async-ops.h) seems to abort
all transfer

5) it *seems* (after some debugging, and looking at nautilus code) that the
progress_sync_callback is the callback that should pass the user descision to
gnome_vfs (please check this first)