Replace WT_PM_REC_SPLIT with WT_PM_REC_MULTIBLOCK: "split" no longer has
meaning outside the WT_PAGE_MODIFY structure, reconciliation doesn't
split pages, it creates single- or multi-block written blocks.
Don't drop core if there weren't any worker threads configured.
Merge branch 'develop' into new-split
update
Fix a comment, split pages don't ever surface any more.
move the eviction routines so they're together.
Add WT_PAGE_IS_INTERNAL, returns true/false if dealing with an internal
tree page.