Chapter 9 / 20..21 - little changed

Note: The old stress test still fails / crashes when the
test executable is run repeatedly in an endless loop.
Chapter 9 / 22 - small change

Note: The old stress test still fails / crashes when the
test executable is run repeatedly in an endless loop.
Chapter 9 / 23 - slow reading fix

Note: The old stress test still fails / crashes when the
test executable is run repeatedly in an endless loop.
Chapter 9 / 24 - additional performance test

Note: The old stress test still fails / crashes when the
test executable is run repeatedly in an endless loop.
Chapter 9 / 25 - additional test now with *10

Note: The old stress test now hangs.
Chapter 9 / 26 - small refactoring

Note: The old stress still appears to hang.
Chapter 9 / 27 - undo some of previous changes, refactor

Note: The old stress still appears to hang.
Chapter 9 / 28

Notes:
1) LocationOf / VirtualLocationOf no long hang,
   since reduced number of users to 50k again.
2) The old stress test still fails.