The test itself is not faulty. The testcase timeout
problem happens if this IMHO mid size resource
(space in vardir, virtual memory, amount of disk I/O)
consuming test meets a weak (excessive disk I/O caused
by parallel applications or paging) testing box.

The modifications:
- Move the most time and disk I/O consuming subtest
  for Bug 1820 into its own script (multi_update2)
  This will reduce the likelihood that we exceed the
  testcase timeout.
- Replace error numbers with error names
- Minor improvements of the formatting

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