Title: Substitution of message passing with variable
Goal: Reject merging an expression that contains subexpressions with side effects.
Parameters:
    [   {file,"ref_rectuple.erl"},
        {posrange,{83,95}},
        {varname,"M"} ].
Documentation:
 The selection is "Pid ! {A+B>C}".
 Since the selection contains side effects (message passing),
 merging is not possible.
