Grammar fix

Submitted by:	Warren Block wblock AT wonkity.com
Simplify the way the end of a singly linked list is followed (for adding
items), so it is more obvious that we aren't going to indirect through
a NULL pointer.

PR:		144723
Submitted by:	Garrett Cooper <yaneurabeya at gmail.com>
Obtained from:	NetBSD r1.19
MFC after:	2 weeks