Show changes to the column cache when PRAGMA vdbe_addoptrace=ON is set.
Remove an unnecessary column-cache flush.  Add another test case to the
speedtest1.c program to accentuate the benefit of not flushing the cache at
that point.
Remove an unnecessary column-cache flush operation.  Add code to trace the
column cache when compiled with SQLITE_DEBUG and using
PRAGMA vdbe_addoptrace=ON.
Omit one or more pointless instructions that occur in between OP_NoConflict
and OP_Halt.
Omit an unnecessary OP_Null opcode from UPDATE.