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)