(io_connect): Changed interface, to take an io_callback instead of
a continuation. The caller has to use make_connect_callback to get
the old functionality.
(io_connect_local): Adapted to new io_conenct interface, and call
make_connect_list_callback.
* src/client_x11.c (channel_open_x11): Likewise.
* src/io_commands.c (do_connect): Likewise.

Rev: src/io_commands.c:1.62