Exercise the various debugging features of the PMSD front end.

sdr> /// Direct access to DanceState object:
sdr> /ds.currentTime()
0/1
sdr> ///
sdr> /// Recursive invocation:
sdr> /const PMSD=net.cscott.sdr.PMSD;
sdr> /PMSD.scrub(PMSD.runTest("<inner>", "sdr> /'whee!'"))
|sdr> /'whee!'
|whee!
sdr> ///
sdr> /// Passing state down to nested invocations
sdr> /this
[object State]
sdr> /a="shared state";
shared state
sdr> /list=java.util.Arrays.asList; undefined;
sdr> /PMSD.scrub(PMSD.runTest(this, "<inner>", list("sdr> /a")));
|sdr> /a
|shared state
sdr> ///
sdr> /// Careful about /exit commands in nested invocations!
sdr> /PMSD.scrub(PMSD.runTest(this, "<inner>", list("sdr> /exit")));
|sdr> /exit
sdr> ///
sdr> /// We shouldn't have exited above.
sdr> /// *Now* exit:
sdr> /exit