Sue's review of changes to cell.i, ref #600.
Go back to using WT_CLEAR on WT_ITEM.  Sue's measurements says it's no slower, and it removes a 64-bit conversion warning.
Make it clear that projections are only supported on table and index cursor types.
typo
Pass the collator reference instead of the Btree handle to the "standard"
lexical comparison functions, then everybody can use the same macros.