aysnc functions v. callback_data

[Murray Cumming <murrayc murrayc com>]

It looks like the async function needs extra destroy_callbacks

For instance,

in gnome_vfs_async_open(), we would normally release the callback_data
when the callback is called, because we assume that the callback will
only be called once. But if someone calls gnome_vfs_async_cancel() then
the callback_data will never be released, because the callback will
never be called.

So do we need new versions of these functions?

http://cvs.gnome.org/viewcvs/gnome-vfs/libgnomevfs/gnome-vfs-async-ops.h?view=markup