work in progress, added method for redirecting stream to optional
data-shapers.
It should also be possible to let those data-shapers output the found
results directly to screen. That way we achieve a much better use of
internal memory because we no longer have to buffer results.
The datashaper get the stream and the number of bytes they are allowed to
get with fgets and after they are done imap_fetch can continue processing
the rest of the data which is still waiting for process on the stream.
Note, it only works for literal values. Body parts are always returned as
literal.