Fixes situations where the remote 'guix build' is invoked before the
.drv has been completely copied, as reported at
<https://lists.gnu.org/archive/html/guix-devel/2014-04/msg00174.html>.
In some cases 'send-files' would return before the other end is done
importing the files, and so the subsequent 'guix build' invocation would
just miss the .drv file it refers to.
* guix/utils.scm (call-with-decompressed-port): Don't close PORT.
(call-with-compressed-output-port): Likewise.
* tests/utils.scm ("compressed-output-port + decompressed-port"): Adjust
accordingly.
* guix/scripts/offload.scm (send-files): Add explicit (close-pipe pipe)
call.
(retrieve-files): Likewise.
30ce8012cd