Restructure the disk image checking functions so there's an easy way to
verify disk images where we don't have an associated length.
Write out the "correct" WT_UPDATE value, even if we're saving/restoring
the entire WT_UPDATE list.  The reason is we have to write something
(the key needs to appear on the page), and the original value may be
gone (imagine an overflow item that's been deleted, that is, the backing
blocks have been freed and the cell type changed to WT_CELL_VALUE_OVFL_RM).
whitespace, try and make the local variable declarations consistent.