offload: Gracefully report connection failures.

* guix/scripts/offload.scm (open-ssh-session): Check the return value of
'connect!'.  Call 'leave' when it's not 'ok.

store: Increase buffering for the '%stderr-write' upcall.

* guix/store.scm (process-stderr) <%stderr-write>: Pass #:buffer-size to
'dump-port'.

daemon: Buffer data sent to clients by the 'export-path' RPC.

Before that we'd have STDERR_WRITE round trips for very small amounts of
data, ranging from a few bytes for the metadata of nars to the size of
one file being exported.

With this change, something like:

  guix archive --export /gnu/store/5rrsbaghh5ix1vjcicsl60gsxilhjnf2-coreutils-8.25 | dd of=/dev/null

reports a throughput of 35 MB/s instead of 25 MB/s before.

* nix/nix-daemon/nix-daemon.cc (TunnelSink): Inherit from 'BufferedSink'
rather than 'Sink'.  Rename 'operator ()' to 'write'.
(performOp) <wopExportPath>: Add 'sink.flush' call.

offload: Warn about the lack of zlib support.

* guix/scripts/offload.scm (guix-offload): Print a warning when
'zlib-support?' returns false.

offload: Remove redundant call to 'topologically-sorted' in 'send-file'.

* guix/scripts/offload.scm (send-files): Remove call to
'topologically-sorted'.

gnu: Add uget.

* gnu/packages/bittorrent.scm (uget): New variable.

gnu: ardour: Update to 5.5.

* gnu/packages/audio.scm (ardour): Update to 5.5.

gnu: python-gst: Update to 1.10.2.

* gnu/packages/gstreamer.scm (python-gst): Update to 1.10.2.

gnu: gst-libav: Update to 1.10.2.

* gnu/packages/gstreamer.scm (gst-libav): Update to 1.10.2.

gnu: gst-plugins-ugly: Update to 1.10.2.

* gnu/packages/gstreamer.scm (gst-plugins-ugly): Update to 1.10.2.

gnu: gst-plugins-bad: Update to 1.10.2.

* gnu/packages/gstreamer.scm (gst-plugins-bad): Update to 1.10.2.

gnu: gst-plugins-good: Update to 1.10.2.

* gnu/packages/gstreamer.scm (gst-plugins-good): Update to 1.10.2.
[source]: Remove patches.
* gnu/packages/patches/gst-plugins-good-fix-crashes.patch,
gnu/packages/patches/gst-plugins-good-fix-invalid-read.patch,
gnu/packages/patches/gst-plugins-good-fix-signedness.patch,
gnu/packages/patches/gst-plugins-good-flic-bounds-check.patch: Remove files.
* gnu/local.mk (dist_patch_DATA): Remove them.

gnu: gst-plugins-base: Update to 1.10.2.

* gnu/packages/gstreamer.scm (gst-plugins-base): Update to 1.10.2.

gnu: gstreamer: Update to 1.10.2.

* gnu/packages/gstreamer.scm (gstreamer): Update to 1.10.2.

gnu: perl-catalyst-action-rest: Change to new uri.

This is a followup to abafd66d04c10fad77a8751fcc3a4dda192c6570.

* gnu/packages/web.scm (perl-catalyst-action-rest)[source]: Update to
new source uri.

gnu: perl-catalyst-view-tt: Change source uri.

This is a followup to 776ca1cb223eb8ec439c7979d5440d5e5fbcaae0.

* gnu/packages/web.scm (perl-catalyst-view-tt)[source]: Change to new
source uri.

gnu: perl-http-server-simple: Change source uri.

This is a followup to 5b3646f100c112f5d43e55393a9be5b2b3647983.

* gnu/packages/web.scm (perl-http-server-simple)[source]: Update to new
source uri.

gnu: perl-http-message: Update URLs.

* gnu/packages/web.scm (perl-http-message)[source]: Update URL.
[home-page]: Likewise.

services: cups: Follow symlinks when installing extensions.

* gnu/services/cups.scm (union-directory): Use "stat" when calling
"find-files" to follow symlinks.

gnu: nasm: Update to 2.12.02.

* gnu/packages/assembly.scm (nasm): Update to 2.12.02.