Provide better error messages for `operator`s

[e-kayrakli]

Here are some cases that can use better error messages:

1. proc type nature of operators could be incorporated into error messages

record myRec {
  var x: int;

  operator +(a) {return x+a; }
}

var r: myRec;

writeln(r+1);

says

error: unresolved call '+(myRec, 1)'

I'd like our compiler to remind me that an operator is a type method where the receiver is a type. I don't know how it thinks x is of type myRec either, but there must be some confusion about the receiver, I think

2. operators with wrong number of arguments simply aren't resolved and dropped

but they should cause error messages, because their existence probably indicates a not-so-innocent mistake in code that can turn up as more difficult errors:

record myRec {
  var x: int;

  // I wrote the following which resulted in unresolved call later, 
  operator +(a) {return a; }

  // ... b/c what I needed was:
  operator +(a, b:int) {return b; }

  // I could also write:
  operator +(a,b,c) {return a+b+c; }
}

var r: myRec;

writeln(r+1);

The first and the last methods there should have been caught by the compiler. I think they should be errors.