now a functions with more than one polymorphic arguments are relative fragile due missing casting to most common type. Some our "functions" like "coalesce" can do it, so it is surprising for our users.
our custom polymorphic function foo(anyelement, anyelement) working well for
foo(10,20) or foo(10.1, 20.1), but not for foo(10, 20.1)
I am thinking, so we can add a searching most common type stage without breaking to backing compatibility.
