Use dhandle hash lists in more places.  Adjust sweep timings. #1460
Extend time in test_sweep01.py. #1460
Switch to stashing the metadata dhandle, not the btree.

Also update checkpoint to use the saved handle instead of
searching for it again.
Ensure metadata table is open at start of checkpoints.
Remove redundant change from dhandle hashing.
Merge branch 'develop' into dhandle-hash
Add a few more sweep stats to understand why the test sometimes fails.
Increase test time to 120 seconds.
Update the swept handles statistic any time we close the underlying handle, regardless of whether a session still references the data handle.

reds #1460, #1466
Even if we don't track any overflow pages during our read of the file,
we still have to process the list of pages looking for leaf pages that
reference unavailable overflow pages, no overflow pages doesn't imply
there are no references to overflow pages.
If we race with the logging thread and get to __wt_logmgr_destroy()
while __log_archive_once() is still using conn->log_path, we can free
it out from under the running server. If there's a logging thread
running, don't free conn->log_path until we've joined that thread.
Reference #1480.
whitespace
We don't need to store double quotes as the default value for
strings, an empty value is sufficient.
Merge branch 'develop' into dhandle-hash

Conflicts:
	test/suite/test_sweep01.py
Merge pull request #1466 from wiredtiger/dhandle-hash

Use dhandle hash lists in more places.  Adjust sweep timings. #1460