make custom buttons possible with html_btn() without the need of global $lang (more consistent with tpl_pagelink())

The media options dialog has currently an open bug regarding the
behavior of the nolink option. Additionally will wrong syntax be
inserted when using Internet Explorer < 8. Since this can't be
fixed on time, this patch disables the media options for the release.

de / typo fix

SafeFN encoding now always end the encoding block by appending a dot at the end of the file name. This is necessary since the file name may get an extension which is not encoded.

The redirect target URL is constructed with escaped ampersands since b6258081.
Thanks to Chris Tapp for pointing out.