warn on deprecated features (#2726)

- `function.arguments`
- `function.callers`

fixes #2719

lib/compress.js

@@ -5461,6 +5461,14 @@ merge(Compressor.prototype, {
     });
 
     OPT(AST_Dot, function(self, compressor){
+        if (self.property == "arguments" || self.property == "caller") {
+            compressor.warn("Function.protoype.{prop} not supported [{file}:{line},{col}]", {
+                prop: self.property,
+                file: self.start.file,
+                line: self.start.line,
+                col: self.start.col
+            });
+        }
         var def = self.resolve_defines(compressor);
         if (def) {
             return def.optimize(compressor);