While 769130f51a did fix one issue, it introduced another by changing the
logic related to the new SignalTracker. The original logic (introduced in
9ad388c5bf) was:
-> in 'leave(Signal)', only call 'disconnect'
-> in 'leaveAll()', call 'disconnect' and 'disconnectTracker'
But 769130f51a inverted this, calling 'disconnectTracker' in both cases but
only 'disconnect' in the 'leaveAll()' case, which would leave unattached signals
around after calling 'leave(Signal)'.
This fix not only repairs the logic, but renames the ambiguous 'disconnect'
boolean to something more explicit: 'withTracker'.
