Content-Range uses space after bytes

Our test expected "Content-Range: bytes=0-N", but this is incorrect.
The RFC-2616 14.16 clearly says:
  bytes-unit SP byte-range-resp-spec "/" ( instance-length | "*" )

This is different from Ranges where bytes=0-N is specified.
The wonders of Web standards!

If a version of swob sent the equal sign previously, it was wrong,
but now corrected.