improve error messages (#1506)

- better inheritance of `Error` sub-classes
- mark parse error against source in CLI

closes #235
closes #348
closes #524
closes #1356
closes #1405

lib/utils.js

@@ -78,13 +78,28 @@ function repeat_string(str, i) {
     return d;
 };
 
+function configure_error_stack(fn) {
+    Object.defineProperty(fn.prototype, "stack", {
+        get: function() {
+            var err = new Error(this.message);
+            err.name = this.name;
+            try {
+                throw err;
+            } catch(e) {
+                return e.stack;
+            }
+        }
+    });
+}
+
 function DefaultsError(msg, defs) {
-    Error.call(this, msg);
-    this.msg = msg;
+    this.message = msg;
     this.defs = defs;
 };
 DefaultsError.prototype = Object.create(Error.prototype);
 DefaultsError.prototype.constructor = DefaultsError;
+DefaultsError.prototype.name = "DefaultsError";
+configure_error_stack(DefaultsError);
 
 DefaultsError.croak = function(msg, defs) {
     throw new DefaultsError(msg, defs);