fixed upstream by:

commit 419b34bb2e60c54d3258c01d9d05a288c47649f2
Author: Tomoki Sekiyama <tomoki.sekiyama>
Date:   Wed Aug 7 19:04:18 2013 -0400

    VirtualCharDevice: Enable channels with char devices other than spicevmc
    
    Currently, virt-manager supports adding spicevmc channel, and cannot add
    channels with char device backends like pty or unix, which is often used by
    guest agents. On the other hand, spicevmc shows up for serial and parallel
    devices, that causes an error if chosen.
    
    This enables virt-manager to add channels with a char device backend other
    than spicevmc, and hides spicevmc from non-channel devices.
    
    Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama>