Re-add required properties. Fixes #61.

lib/mess/tree/definition.js

@@ -79,6 +79,17 @@ tree.Definition.prototype.toXML = function(env) {
         sym = sym[0];
     }
 
+    if (sym) {
+        if (reqfail = tree.Reference.requiredProperties(
+            sym,
+            this.unique_rules())) {
+            env.error({
+                message: reqfail,
+                index: this.unique_rules()[0] && this.unique_rules()[0].index
+            });
+        }
+    }
+
     var symname = sym ? sym.charAt(0).toUpperCase()
         + sym.slice(1).replace(/\-./, function(str) {
         return str[1].toUpperCase();

lib/mess/tree/reference.js

@@ -620,8 +620,11 @@ tree.Reference.requiredPropertyList = function(symbolizer_name) {
     return properties;
 };
 
-tree.Reference.requiredProperties = function(symbolizer_name, properties) {
+tree.Reference.requiredProperties = function(symbolizer_name, rules) {
     var req = tree.Reference.requiredPropertyList(symbolizer_name);
+    var properties = rules.map(function(r) {
+        return r.name;
+    });
     for (i in req) {
         if (properties.indexOf(req[i]) === -1) {
             return 'Property ' + req[i] + ' required for defining '