adjust range request: send correct boundary information

So far we just concatenated all byte ragne parts , now we send
the correct boundaries according to
http://www.w3.org/Protocols/rfc1341/7_2_Multipart.html
add correction for multirange requests

1. implement the range boundaries
2. return the size of each part and build into the request

This makes the streaming a lot more complicated, with
an additional wrapper function around the stream.
Also, more cases have to be differentiated in the
get_cdmi_file_obj function.
reorder the range request list and cut range size at file size

it's simple reordering for now, ordering them by start.
overlapping ranges are still allowed and lead to seeking back.