[for the 0.6.x branch]

* (important) noted by Nikos: 
  The keydb search is not thread safe because. Needs a review.
  Actually other parts suffer from the same problem. 
  Because the keydb is only open once, concurrent key readings will
  result in an unpredictable result.

* at several places the internal structure of the code needs to
  be revamped.
  
* cdk_file_decrypt and friends should return the output file name
  because it might be possible that the real output is different
  than the suggested. Or we need to force the code to use the given
  output file.
  
* stream.c: enhance the EOF detection

* We still need more tests, especially for the 'exotic' and less
  used interfaces and functions.


** Things we need to migrate stepwise ***
The old stream code has lots of problems. And most of the 
complexity is not needed. With the new reader and writer
concept, we can add new filters more easily and there are
no temp files or multiple runs on the same data.

 
** Known problems to fix **

* some parts of the code does not seem to work on W32 or 
  better it probably needs some adjustments.
