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

diff --cc builtin/submodule--helper.c
Simple merge