Ignore child pages without an address in column stores: in-memory splits can hit this case.

refs #900
Merge branch 'develop' into new-split
Add a comment, we need to revisit this code.
Simplify __rec_review: there's no eviction walk flag left, so looking
for it in the stack of parent pages is pretty pointless.

Lock internal pages during checkpoint to ensure that we never see a
page being split.  I don't like holding this lock, but I don't see
an alternative at the moment -- it's really unlikely we'd see a split
because you have to write dirty pages to cause splits, and checkpoints
have already turned off dirty page writes, but the split could race
with checking the checkpoint flag.

Don't set WT_SKIP_UPDATE_RESTORE on anything other than the top-level
eviction page (I don't see why it wouldn't work, but it's pointless).

Rename WT_EVICTION_SERVER_LOCKED to WT_EVICTION_LOCKED, there's no
server anymore.