dbus/jack_control:
The `jack_control` script is dbus specific and not part of the original
jack tools. As the files offered by jack-example-tools are now
optionally not built, the script needs to be made available from a
location, that is not ignored when omitting the build of
jack-example-tools files.
The main loop might be blocked by `data_ready` when JACK server dies
while the program is running.
To reproduce the problem:
1. Start JACK server
2. Run `jack_midi_dump`
3. Stop JACK server
4. Press Ctrl-C in `jack_midi_dump` to send SIGINT.
5. Observe that the program doesn't stop and stuck in the main loop.
This patch forces the `data_ready` to be signaled in the signal handler
to prevent indefinite waiting.