More hickups found due to the mimetester; pre push.

 - the_mime_parser (): we need to know where parse_MimeHeaders() finds the end of the headers.
 - the_mime_parser (): don't move the pointer around just to count up to the end-pointer. this can be done by pointer substraction.
 - parse_MimeHeaders (): move the parameter so our caller gets to know what we read
 - parse_MimeHeaders (): if (ptr >= content_end)  after reading is probably a bug (also there in stable..), that makes us fail to read the last line, if. move it to the end of the pointer.
 - don't call strchr twice; remember & evaluate the first result
 - stripping the disposition-header can be done right where we found it.