Document "tdnam" keyword to ps(1), and add "tdname" alias.

MFC after:	2 weeks
Sponsored by:	DARPA, AFRL

bin/ps/keyword.c

@@ -201,6 +201,7 @@ static VAR var[] = {
 	{"tdev", "TDEV", NULL, "terminal-device", 0, tdev, 0, CHAR, NULL, 0},
 	{"tdnam", "TDNAM", NULL, "terminal-device-name", LJUST, tdnam, 0, CHAR,
 	    NULL, 0},
+	{"tdname", "", "tdnam", NULL, 0, NULL, 0, CHAR, NULL, 0},
 	{"time", "TIME", NULL, "cpu-time", USER, cputime, 0, CHAR, NULL, 0},
 	{"tpgid", "TPGID", NULL, "terminal-process-gid", 0, kvar,
 	    KOFF(ki_tpgid), UINT, PIDFMT, 0},

bin/ps/ps.1

@@ -29,7 +29,7 @@
 .\"     @(#)ps.1	8.3 (Berkeley) 4/18/94
 .\" $FreeBSD$
 .\"
-.Dd September 7, 2017
+.Dd October 9, 2017
 .Dt PS 1
 .Os
 .Sh NAME
@@ -675,6 +675,9 @@ saved UID from a setuid executable
 accumulated system CPU time
 .It Cm tdaddr
 thread address
+.It Cm tdnam
+thread name (alias
+.Cm tdname )
 .It Cm tdev
 control terminal device number
 .It Cm time