Ensure that tailproc is set for the last process in an Eshell pipeline

Ensure that tailproc is set for the last process in an Eshell pipeline

In particular, this used to fail for pipelines where the last process
in the pipeline came from the first element of the pipeline. This
could happen when a process was piped to an ordinary Lisp function,
like in '*echo hi | echo bye'.

* lisp/eshell/esh-cmd.el (eshell-do-pipelines): Set the tailproc even
for the first process in the pipeline.

* test/lisp/eshell/eshell-tests.el (eshell-test/pipe-tailproc): New
test.