MFC revisions 268860, 268863:
r268860: Minor enhancements, bug fixes, and man-page adjustments.
r268863: Bump .Dd in manual

Reported by:	lme
Approved by:	re (gjb)
MFC revisions 262864-262865, 263114, 267970:
r262864: Stop pw(8) from segfaulting when given certain input (julian)
r262865: Part 2 of bug 187310 (julian)
r263114: Fix pw(8) edge-case deletion of group "username" on userdel
r267970: Fix infinite-loop during deletion of users from groups

PR:		187310, 169471, 191427
Submitted by:	Voradesh Yenbut, Alexander Pyhalov, Kim Shrier
Obtained from:	bug
Approved by:	re (gjb)