Comet parameter: add_C_cysteine
         
         - Specify a static modification to the residue C.
         
 - The specified mass is added to the unmodified mass of C.
         
 - The default value is "0.0" if this parameter is missing *except*
         if Comet is compiled with the
         Crux flag on.
         For Crux compilation, the default value is "57.021464" if this parameter is missing.
         
 
         Example:
         
add_C_cysteine = 57.021464