Backed out changeset 21e52e54ea4d
Merge branch 'develop' into fast-checkpoints
Re-enable fast checkpoints.
Merge branch 'develop' into fast-checkpoints
Merge branch 'develop' into fast-checkpoints
Merge branch 'develop' into fast-checkpoints
Merge branch 'develop' into fast-checkpoints
Merge branch 'develop' into fast-checkpoints
Don't try to "help" checkpoints from eviction threads: we can't get the snapshot right, so this was only ever approximate, and the checkpoint has just written all the dirty pages as part of the "write leaves" step, so if we can't find clean pages, it's unlikely we'll be able to write them correctly.  Remove the WT_SKIP_UPDATE_OK flag: it is no longer needed.

refs #963
Merge pull request #963 from wiredtiger/fast-checkpoints

Fix fast checkpoints