Fixes for WT_INSERT objects with invisible WT_UPDATE objects.  For
row-store types, it means there's no exact match because row-store page
objects cannot have the same key as a WT_INSERT object.  For
column-store types, column-store page object keys can be identical to
WT_INSERT object keys, use the returned slot to figure it out.

Simplify the test for empty pages, we can test for both empty and
"beyond the end" in one test.

Reorder the search-near code, check for a valid key/value pair returned
from the search function before checking for implicitly created rows.