Bugfix: Disable handling SIGPIPE

We've disabled handling SIGPIPE again. Turns out, writing to broken TCP
connections also raised SIGPIPE, so restic exits on the first write to a
broken connection. Instead, restic should retry the request.

https://github.com/restic/restic/pull/1459
https://github.com/restic/restic/issues/1457
https://github.com/restic/restic/issues/1466
