Split right

Not ready for merge.
@agorrod, @michaelcahill: it turns out fixing up the original page on error isn't hard, I just did the same trick I did on the new page, attach the moved insert item to the end of the level 0 list and ignore any previous skip list depth it might have had.

I changed my test program to fail every 5th split attempt and the recovery code appears to work correctly, but I'd appreciate someone taking a close look at the change in c5d0534.