Require the SQLITE_ENABLE_RTREE compile-time option in speedtest1.c in order
to enable the R-Tree tests.
Simplification to the insertCell() routine in btree.c, resulting in a
performance boost and a very small size decrease.  It turns out that the
extra work involved in sometimes avoiding an memcpy() of the first four bytes
of a record takes more time than just unconditionally copying those
four bytes.
Performance optimization and very slight size reduction for OP_Column.