Throw error when compiling multiple roots

Closes #338

src/Compiler.js

@@ -191,6 +191,11 @@ Compiler.prototype = {
     var index = 0,
         template,
         parent = templateElement.parent();
+    if (templateElement.length > 1) {
+      // https://github.com/angular/angular.js/issues/338
+      throw Error("Cannot compile multiple element roots: " +
+          jqLite('<div>').append(templateElement.clone()).html());
+    }
     if (parent && parent[0]) {
       parent = parent[0];
       for(var i = 0; i < parent.childNodes.length; i++) {