ash: simplify EOF/newline handling in list parser

ash: simplify EOF/newline handling in list parser

Processing of here documents in ash has had a couple of breakages
which are now the subject of tests.  This commit should fix both.

It is based on the following commit in dash git by Herbert Xu:

   <7c245aa> [PARSER] Simplify EOF/newline handling in list parser

(See git://git.kernel.org/pub/scm/utils/dash/dash.git)

Reported-by: Natanael Copa <ncopa@alpinelinux.org>
Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>