On platforms where "git fetch" is killed with SIGPIPE (e.g. OSX),
the upload-pack that runs on the other end that hangs up after
detecting an error could cause "git fetch" to die with a signal,
which led to a flakey test.  "git fetch" now ignores SIGPIPE during
the network portion of its operation (this is not a problem as we
check the return status from our write(2)s).

* jk/no-sigpipe-during-network-transport:
  fetch: ignore SIGPIPE during network operation
  fetch: avoid calling write_or_die()