Move third-party TinyMCE out of soc/content/js and into the application image root, like other third-party code. Update the app.yaml.template to add /tiny_mce as a source of static content.

.mcePageBreak {display:block;border:0;width:100%;height:12px;border-top:1px dotted #ccc;margin-top:15px;background:#fff url(../img/pagebreak.gif) no-repeat center top;}