Add WT_SESSION use-countet to WT_DATA_HANDLEs
Only sweep session handle list for dead handles a few times a minute.
cleanup some unused variables.
lint
Use BILLION instead of many zeroes in wtperf.
Don't bump the scan count if we can use a cached transactional snapshot.

refs #777
Replace two thread modes (individual insert, read & update threads,
and "job-mix" threads) with a single configuration for a thread
count and workload expressed as a ratio of inserts, reads and updates.
Ref #775.
The rest of the changes for #775: we can now support multiple, entirely
unrelated workloads.
Update the canned configurations inside of the wtperf source code.
Update the runners again: now that threads takes groups of options,
you can't do:

	threads=(count=1,read=1)

you have to do:

	threads=((count=1,read=1))

instead, doubling the parentheses.
Michael notes the runner scripts changes were wrong, we need to have
dedicated threads for inserts, reads, and updates, that's how they
currently work.  #783
Add a new lsm_chunk_max configuration option to WT_SESSION->create.
Respond to review comments for lsm_chunk_max configuration option.
Don't wait forever in log archive in case a notification gets lost.
Cleanup the condition wait calls to make the intent clearer.
Tweak the test/bloom parameters to more closely match some real tests.
Fix __wt_cursor_close so it can decrement the data handle cursor count statistic correctly.  Previously it was clearing `session->dhandle` on entry, so the stat decrement never happened.
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semantic sugar -- make leading comments match standard style, minor function
shuffling.
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