Give privilege to users in TerminalServerAdmins

Revives the currently unused TerminalServerAdmins group.

Users in this group will eventually have special privileges for session
management. Currently, members of this group will be allowed to
list all sessions with the xrdp-sesadmin command.

docs/man/sesman.ini.5.in

@@ -271,8 +271,9 @@ login for all users is enabled.
 
 .TP
 \fBTerminalServerAdmins\fR=\fIgroup\fR
-\fIThis option is currently ignored!\fR Only members of this group can
-have session management rights.
+Members of this group can use the \fBxrdp-sesadmin\fR command to
+administer sessions started by other users. The root user is always
+considered to be in this group.
 
 .TP
 \fBRestrictOutboundClipboard\fR=\fI[all|none|text|file|image]\fR
@@ -334,8 +335,16 @@ To keep compatibility, the following aliases are also available.
 
 .TP
 \fBAlwaysGroupCheck\fR=\fI[true|false]\fR
-If set to \fB1\fR, \fBtrue\fR or \fByes\fR, require group membership even
-if the group specified in \fBTerminalServerUsers\fR doesn't exist.
+If set to \fB1\fR, \fBtrue\fR or \fByes\fR:-
+.RS
+.HP 3
+- For normal logins, require group membership even if the group specified
+in \fBTerminalServerUsers\fR doesn't exist.
+.HP 3
+- An error message may be generated when any user authenticates
+if the group specified in \fBTerminalServerAdmins\fR doesn't exist. This is
+because the system is unable to check whether the user is an administrator.
+.RE
 
 .TP
 \fBAllowAlternateShell\fR=\fI[true|false]\fR

docs/man/xrdp-sesadmin.8.in

@@ -37,7 +37,8 @@ Valid commands are:
 .RS 4
 .TP
 .B list
-List active sessions for the current user.
+List active sessions for the current user.  Members of the
+\fBTerminalServerAdmins\fR group can view active sessions for all users.
 .TP
 .BI kill: sid
 Kills the session specified the given \fIsession id\fP.