based on what generators provide via ktrader, includes caching the mimetype list
- handling of compressed files added too
- both fucntions basedo kviewshell's version that Wilfried Huss suggested, although with 
  significant remodelling by myself, still i see no problem on adding relevant copyrights
  to this file for the original functions' author just tell me how he/she is

svn path=/trunk/playground/graphics/oKular/kpdf/; revision=434859