When we get notified of an "active-input/output-device" change by gvc, we have
to update our respective combo box to reflect that change. Obviously, this in
turn shouldn't trigger our own signal handler for changes on that combo box,
that signal handler is only meant to handle the user interacting with the combo
box.
So block our signal handlers when we update the combo box to respond to changes
from the gvc side.
This fixes a recursive call to gvc_mixer_control_change_input/output() when we
get notified about an input/output change from gvc itself.
a74bc5a84d
