Previously, code using directly (guix build download) was still affected
by <http://bugs.gnu.org/15368>. This includes source derivations, the
'guix download' command, and (guix gnu-maintenance).
'guix substitute' was unaffected since it used (guix http-client), which
already had the fix.
* guix/http-client.scm (open-socket-for-uri): Remove.
(http-fetch): Remove #:buffered? argument to 'open-socket-for-uri';
use 'setvbuf' instead.
* guix/scripts/substitute.scm (fetch): Likewise.
* guix/build/download.scm (open-socket-for-uri): New procedure, taken
from guix/http-client.scm, but without the #:buffered? parameter.
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