Fix the check for whether updates can be evicted, vs whether the page is marked clean.
fix a comment
Use hazard references to prevent child pages being evicted during reconciliation of their parent.

refs #896, #898, #899
Merge branch 'new-split' into evict-visible-changes

Conflicts:
	src/btree/rec_write.c
Read an update's transaction ID into a local variable to avoid racing with a rollback.  Matches f188344027ec72921b9d2dd9e473bf05d3ce6b24 on develop.
Cleanup of the fix, implement review feedback and match Keith's version in 4f182499fd097cdeaede49907299b6f32d30af71.
Merge pull request #900 from wiredtiger/rec-child-hazard

Use hazard references to prevent child pages being evicted during reconciliation of their parent
Merge branch 'develop' into evict-visible-changes

Conflicts:
	src/btree/rec_write.c
Merge pull request #895 from wiredtiger/evict-visible-changes

Fix the check for whether updates can be evicted, vs whether the page is marked clean.