Make run-time statistics optional, defaulted to "off".

Change statistics_log to pay attention to the new statistics flag
(this means you can turn statistics logging on/off by reconfiguring
the statistics flag).

Don't allocation statistics structures separately from the enclosing
objects, it simplifies error handling a lot.

Fix a bug in re-configuration, we should only review the application-
specified values, and verbose configuration wasn't doing that.
Merge branch 'develop' into statistics

Conflicts:
	src/config/config_def.c
	test/format/wts.c
Run more of the wiredtiger_open calls by closing previously opened handles.
Change it so that statistics_log configures statistics as well.
Merge pull request #463 from wiredtiger/statistics

Make run-time statistics optional.