Merge libedit fixes from NetBSD

Add trailing NULL's to the varargs functions as required.
(John Spencer)

readline.c r1.106

Bounds search for reallocated index, from OpenBSD via Andreas Fett

map.c 1.34
map.h 1.10
parse.c 1.27
read.c 1.71

This is a direct commit to stable/10 as these changes are included in a
broader sync with NetBSD committed by bapt@ in r276881.

Reviewed by: bapt
Differential Revision: https://reviews.freebsd.org/D1728