Method newOpBefore

\brief Create new PcodeOp with 2 or 3 given operands The new op will have a \e unique space output Varnode and will be inserted before the given \e follow op. \param follow is the \e follow up to insert the new PcodeOp before \param opc is the op-code of the new PcodeOp \param in1 is the first operand \param in2 is the second operand \param in3 is the optional third param \return the new PcodeOp