Apply TinyMCE security fix for CVE-2012-6112

Apply TinyMCE security fix for CVE-2012-6112 from
https://github.com/tinymce/tinymce_spellchecker_php/commit/22910187bfb9edae90c26e10100d8145b505b974.
Merge pull request #5289 from taca/tinymce-CVE-2012-6112/develop