Improve in-memory merge efficiency when there is a lot of forced eviction: focus near the top of a stack of pages, merge as soon as we see a good candidate.
typo
Fix the eviction pass for internal pages: check the local flags: we clear the cache flags after each walk.
Try an in-memory split before forced eviction, also make the "promotion" code for merges apply in more cases than just a single first/last child.
Create real internal pages when merging, if they get big enough.
Merge stacks of split-merge pages, no matter how big.  Once they get big enough, create internal pages even if the parent is a split-merge page.
Merge branch 'develop' into merge-efficiency
If an in-memory split fails, unlock the page.
Fix a "may be uninitialized" warning in zlib.
Merge branch 'develop' into merge-efficiency
Try an in-memory split before evicting big pages: that avoids the tree growing arbitrarily deep for append-only workloads.
Remove WT_MERGE_MAX_REFS -- it was always arbitrary, and now when we create an internal page with more than 100 children, it won't be marked split merge, so we won't merge it again.
Merge pull request #851 from wiredtiger/merge-efficiency

Improve in-memory merge efficiency when there is a lot of forced eviction