In batch mode, SIGPIPEs can cause Emacs to abort (bug#66186).
* lisp/eshell/esh-io.el (eshell-output-object-to-target): Update
comment.
* test/lisp/eshell/esh-proc-tests.el
(esh-proc-test/pipeline-connection-type/middle)
(esh-proc-test/pipeline-connection-type/last): Use '(ignore)', since
that causes no output when called with no arguments, thus avoiding a
risky 'process-send-string'.