- pass xfr request data length in network byte order, and receive it as such. receiving this as native data (unpack('H')) would be a bit naive because it may assume some padding.
 - avoid cast as a bonus side effect of the first fix
 - make cmsg space handling more portable.  use CMSG_SPACE when possible; otherwise calculate the space using dummy data
 - overall simplied fd_share code: trying to handle multiple FDs is not correct in terms of API, and in any case we don't need that; verify cmsg_level and cmsg_type on reception; avoid unnecessary data initialization; stop naively assume the exact memory allocation of cmsg_data (assuming no padding) - use cmsg_space() so that padding, if any, will be taken intou account
 - catch the error case of recv_fd failure in XfroutSession.handle() explicitly, and raise an exception


git-svn-id: svn://bind10.isc.org/svn/bind10/trunk@1694 e5f2f494-b856-4b98-b285-d166d9295462