Instantiate a full key for the parent ref of a page during in-memory splits.  The original page's key may have been truncated and may not be valid after the split.

Also, take care to free the original key if it was instantiated, fixing a leak found by address sanitizer.

refs #1419, #1421
Remove stray debugging.
Use the original approach to finding the first key on a page: search the smallest insert list first, then look on the page.
Merge pull request #1422 from wiredtiger/split-ref-key

Instantiate a full key for the parent ref of a page during in-memory splits