Add support for aggregating data-source statistics, currently only
used by the LSM tree.

Add support for automatically updating the list of statistics that
are to be "scaled per second" by statlog.py.
Back out a change that added statistics_log calls to the configs,
that change was just for testing.
Use more verbose names for the various statistics entry flags.
Reverse the sense of the "scale" option, make it "no_scale" instead
(there are 100+ entries that scale, roughly 30 that don't).
Give the LSM tree its own data-source statistics structure back, move
the bloom filter statistics back into that structure.

Change the underlying stat macros to check if statistics are configured
at the lowest (WT_STAT_XXX) levels: this means we potentially check to
see if statistics are configured a lot more (every time a stat field is
updated), but it ensures we don't actually maintain the statistics
unless they're configured.  Trust the compiler will optimize out the
extra tests for configuration.
Be explicit, we're turning on a set of flags.
Add WT_CURSOR_STATS to return a reference to a statistic cursor's stats,
it's a little cleaner when we reach down into the cursor in the LSM code.
Merge branch 'develop' into lsm_stats
Once again, back out the testing change.
Add a comment that the list of graphs we don't want to scale per second
is auto-generated.
typo
As a consequence of the last set of changes, you can't get the cache-size
(which is a statistic), without configuring "statistics" when you open the
database.
Fix a comment, callers of __wt_lsm_tree_get are supposed to already be
holding the schema lock.
We can't hold the schema lock while stat traverses the list of LSM trees
because the LSM statistics code acquires the tree lock, and the LSM
cursor code acquires the tree lock and then acquires the schema lock,
it's a classic deadlock.
Cut-and-paste mistake: don't leave early, without releasing the rest of
the pinned LSM trees.
Expand on some comments.
Merge branch 'develop' into lsm_stats
Merge pull request #520 from wiredtiger/lsm_stats

Add more generic aggregated statistics. Used for LSM at the moment, will be expanded to other data sources in the future.