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.
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