Merge branch 'pw/submodule-process-sigpipe'

When a subprocess to work in a submodule spawned by "git submodule" fails with SIGPIPE, the parent Git process caught the death of it, but gave a generic "failed to work in that submodule", which was misleading. We now behave as if the parent got SIGPIPE and die. * pw/submodule-process-sigpipe: submodule status: propagate SIGPIPE