fix(HtmlParser): ng-content is not a void element

fixes #5563
Closes #5586

modules/angular2/src/compiler/html_tags.ts

@@ -311,7 +311,6 @@ export class HtmlTagDefinition {
 // This implementation does not fully conform to the HTML5 spec.
 var TAG_DEFINITIONS: {[key: string]: HtmlTagDefinition} = {
   'link': new HtmlTagDefinition({isVoid: true}),
-  'ng-content': new HtmlTagDefinition({isVoid: true}),
   'img': new HtmlTagDefinition({isVoid: true}),
   'input': new HtmlTagDefinition({isVoid: true}),
   'hr': new HtmlTagDefinition({isVoid: true}),

modules/angular2/src/compiler/template_parser.ts

@@ -228,6 +228,11 @@ class TemplateParseVisitor implements HtmlAstVisitor {
         hasInlineTemplates ? null : component.findNgContentIndex(elementCssSelector);
     var parsedElement;
     if (preparsedElement.type === PreparsedElementType.NG_CONTENT) {
+      if (isPresent(element.children) && element.children.length > 0) {
+        this._reportError(
+            `<ng-content> element cannot have content. <ng-content> must be immediately followed by </ng-content>`,
+            element.sourceSpan);
+      }
       parsedElement =
           new NgContentAst(this.ngContentCount++, elementNgContentIndex, element.sourceSpan);
     } else if (isTemplateElement) {