Changes to sqlite3VdbeRecordUnpack() to make it slightly smaller and faster.
Reorder the elements of the Mem object for a small size reduction and
performance improvement.
Reduce the number of arguments to RecordCompare functions from 4 to 3,
resulting in a small performance increase.
Remove an unused parameter from sqlite3VdbeIdxRowid().  This is cosmetic
only as the C-compiler optimizers were already omitting this parameter on
amalgamation builds.
Simplification of the OP_Column logic for the case of rows with overflow.
Make sure registers are cleared properly prior to being used to store
the result of an OP_Column operator.
Continuing cleanup of memory register memory allocation handling.