Use one check for whether to try forced eviction in a given session.  Skip eviction of clean pages with modifications that are too recent, unless eviction gets aggressive.
Read threads should not bump the cache read generation: eviction is now responsible for that.  Somehow this part of 30b1a822b26ff0531a0d31aa2895bc98b6f53d88 got lost.
Have the eviction thread update the oldest transaction ID in the system before each walk: we now use that to filter LRU candidates, and if a long-running transaction such as a checkpoint blocks all other threads in the system, the oldest ID has to be updated after the long-running transaction completes.
In python, flush during callbacks to wrute to sys streams. refs #883.
Merge pull request #889 from wiredtiger/python-flush

In python, flush during callbacks to write to sys streams. refs #883.
Fix wtperf make check, and versions in upgrading documentation.
Cut release 2.1.1
Bump version tag to 2.1.2 on develop.
Have wtperf reset cursors when there are multiple tables.  Otherwise, there are always cursors positioned in every session, and the transactional snapshot is never updated.
Simplify __wt_row_key_get a little, fix a comment, move it to live
with the other "get a row-leaf key" functions in btree.i.
Run voxer tests for 5 hours.
Add a multi-table config and shorter voxer configs for Jenkins.
Adjust thread pools for new Jenkins configs.
Add 1b and 4b test configs.
Take a copy of the update transaction ID in reconciliation in case we race with a rollback.  Go straight to aggressive eviction once the cache gets stuck.

refs #894
Merge branch 'develop' into evict-walk-hazard