Add support for timer-specified runs.

Support compaction & backup for single-threaded runs.
Don't update the counters as often, should help with shared cache lines.
Change skip list probability to 1/2 from 1/4.
Put assert-only loop under HAVE_DIAGNOSTIC. #1371
Add checkpoint timer stats. #1374
Fix error wrapper usage.  Change units to msecs. #1374
Allow unicode typed objects in Python with S/s formats.  refs #1187.
Includes tests that trigger the problem.
Revert skip list probability back to 1/4.
Move checkpoint timing code lower and only time full database
checkpoints. #1374
Merge branch 'develop' into checkpoint-timers
Merge pull request #1375 from wiredtiger/checkpoint-timers

Add checkpoint timer stats. #1374
Add a stat macro so can directly access connection statistics' values;
maintain the checkpoint statistics in the WT_CONNECTION_IMPL statistics
structure fields instead of in separate WT_CONNECTION_IMPL fields.
Merge pull request #1377 from wiredtiger/python-unicode

Allow unicode typed objects in Python with S/s formats.  refs #1187.
Merge branch 'develop' into format-timer
Make sure each thread has at least one operation to perform, but not
an arbitrary number.
Do operations if we have a time or an operation count.
Merge pull request #1372 from wiredtiger/format-timer

Format timer
remove tab characters from Python scripts.
When adjusting variable-length sizes, odd things can happen on the encoding boundaries.  Play it safe and iterate until we know the final size.

JIRA-16118
Fix the size adjustment issue by tweaking the encoding of one value so that packed sizes never decrease as values increase.