Method checkCallDoubleUse

\brief Test for legitimate double use of a parameter trial The given trial is a \e putative input to first CALL, but can also trace its data-flow into a second CALL. Return \b false if this leads us to conclude that the trial is not a likely parameter. \param opmatch is the first CALL linked to the trial \param op is the second CALL \param vn is the Varnode parameter for the second CALL \param fl