Correctly treat all assignments with bogus trailing comments.

Correctly treat all assignments with bogus trailing comments.

Before this patch, automake would silently fail to diagnose and
to copy into the output those variable assignments which are
preceded by a comment, and end in backslash newline comment.

* automake.in (read_am_file): When determining whether an
escaped newline followed by a comment is an error, correctly use
the parser state, not the contents of a saved comment, which
could still be carried over from a comment before an assignment.
* NEWS: Update.
* tests/commen11.test: New test.
* tests/Makefile.am: Update.
Report by Karl Berry.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>