Make it possible to associate multiple probes to a single rule.

Make it possible to associate multiple probes to a single rule.

The following syntax, reducing duplication, is now allowed:

END,
interval:hz:2
{
...
}

Rule descriptors are now linked to a list of probe descriptors instead of
a single one.  Enabled kernel probes are now linked to btrace(8) probe
descriptors.

While here stop parsing filter and probe if debug is not enabled.