[ChangeLog]

[ChangeLog]
* NEWS: "groups user" no longer outputs "user :"; you need at least
two users.  "groups" now processes options like --help more compatibly.
* src/groups.sh: Implement the option-processing change.
Handle user and group names with special characters more robustly.
Report write errors instead of exiting silently with status 1.
[doc/ChangeLog]
* coreutils.texi (groups invocation): "groups" no longer prefixes
the output with "user :" unless more than one user is specified.