Any bytes we can skip in a parent page, we can skip in a child page,
the keys are going to have the same set of prefixes.   Ref #595.
Merge branch 'develop' into offsetsearch2
Merge pull request #694 from wiredtiger/offsetsearch2

skip the same prefix bytes on the child page that we skipped on the parent page
Change the default statistics_fast configuration from false to true.