Update contao42 to 4.2.3.

### 4.2.3 (2016-09-06)

* Do not double URL encode the content syndication links.
* Use CSS3 transforms instead of transitions to animate the off-canvas navigation.
* Improve the exception handling when using the resource locator (see #557).
* Correctly reset the filter menu in parent view.
* Support all characters but =!<> and whitespace in simple tokens (see contao/core#8436).
* Check the user's permission when generating links in the picker (see contao/core#8407).
* Handle forward pages without target in the navigation modules (see contao/core#8377).
* Provide the same template variables for downloads and enclosures (see contao/core#8392).
* Handle %n when parsing date formats (see contao/core#8411).
* Fix the module wizard's accessibility (see contao/core#8391).
* Correctly initialize TinyMCE in sub-palettes in Firefox (see contao/core#3673).
* Validate form field names more accurately (see contao/core#8403).
* Correctly show the ctime, mtime and atime of a folder (see contao/core#8408).
* Correctly index changed pages (see contao/core#8439).

(taca)