I discovered that some pyftpdlib [1] tests fail when using poll()
instead of select().
The problem is in asyncore.readwrite() function which erroneously calls
handle_read_event() in case of a POLLPRI event.

The patches modify readwrite() function so that:

- POLLPRI is now treated as synonym for "there is urgent data to read"
so handle_expt_event() is called.
- POLLHUP, POLLERR and POLLINVAL are now treated as synonyms for "the
connection has been closed" (Twisted behaves exactly the same) so
handle_close() is called.

Both pyftpdlib and asyncore tests passed on Linux Debian Etch and
FreeBSD 7.0-RC1.


[1] http://code.google.com/p/pyftpdlib/