Remove the OPFLAG_CLEARCACHE flag from OP_Column.  In its place, change the
P3 parameter of OP_SorterData to be the index of the pseudo-table cursor whose
record header cache is to be cleared.  This gives a small size reduction
and performance increase.
Reduce the CPU load imposed by sqlit3VdbeCursorMoveto() by factoring out
some of its functions and by avoiding unnecessary calls.
Three small optimizations to vdbeaux.c.
Use the padding word in the Mem object as temporary storage for
serial_type value in OP_Record, and thus avoid a redundant computation of
the serial_type for each column.
Optimize a database corruption test inside of the OP_Column opcode.