throw a syntax error if you try to use the fat arrow to define a class constructor.

lib/nodes.js

@@ -739,6 +739,9 @@
         pvar = _e[0];
         func = _e[1];
         if (pvar && pvar.base.value === 'constructor' && func instanceof CodeNode) {
+          if (func.bound) {
+            throw new Error("cannot define a constructor as a bound function.");
+          }
           func.name = className;
           func.body.push(new ReturnNode(literal('this')));
           this.variable = new ValueNode(this.variable);

src/nodes.coffee

@@ -647,6 +647,7 @@ exports.ClassNode: class ClassNode extends BaseNode
     for prop in @properties
       [pvar, func]: [prop.variable, prop.value]
       if pvar and pvar.base.value is 'constructor' and func instanceof CodeNode
+        throw new Error "cannot define a constructor as a bound function." if func.bound
         func.name: className
         func.body.push new ReturnNode literal 'this'
         @variable: new ValueNode @variable