Add the OP_Undef and OP_IsUndef opcodes.  With these, use the first register
in the result register range as the flag to indicate EOF on an INSERT from
a SELECT, rather than allocating a separate boolean register for that task.
Get rid of the OP_Undef and OP_IsUndef opcodes in favor of higher-level
OP_InitCoroutine and OP_EndCoroutine.
Change the OP_InitCoroutine instruction to jump over the co-routine
implementation.
In the TCL bindings, make sure Tcl_AppendResult() is always terminated
by "(char*)0" and not just "0".
Fix redundant definitions of _LARGE_FILE and _LARGEFILE_SOURCE.
Add opcodes OP_InitCoroutine and OP_EndCoroutine.  Use these to remove the
need for separate boolean registers to record when a co-routine has finished.
Change the OP_Trace opcode to OP_Init and give it the ability to jump to the
initialization code at the bottom of the program, thus avoiding the need for
an extra OP_Goto.
Enable constant expression factoring even if no tables are read and no
transaction is started.