adjust cdmi.y for 4-space indentation
implement returning CDMI objects for a directory GET

this is an initial implementation iwth the following goals:
- return CDMI-compliant response for a directory listing
- use streaming for chunked responses

This works, but not too well. Getting a string output
is entangled with the treatment of the content, and we
cannot switch between e.g. compact and pretty printed
json output.
update the cdmi response for directories

Split between creating the single entries and creating
a CDMI response.
The inner function returns a tuple that is either two strings
(key and value) or string and generator function.
Another wrapper contructs a json response from this, concatenating
the entries as they were dict entries.

Beacuse of json's parantheses rule, the inner function must make
sure to surround any strings by "".
fix redirection for directories

now the redirection also includes the query parameters
simplify the cdmi check function

it now uses the request_wants_cdmi fucntion
to perform the check