Mime-parser rework: parse the mime headers of the current container so we can guess...

Mime-parser rework: parse the mime headers of the current container so we can guess the size of the content to jump accross; binary/ascii is used to switch the search algorithm for the next boundary.

 - the old mime parser version skipped empty containers; we do this by hand
 - for some reason the numbers addressing the mimeparts grow different, maybe mixed use of old/new may cause confusion...