- Fix an off-by-one bug in addgroup().

- Fix the error message when setgid() failed.

PR:		bin/161509
Submitted by:	Jeremy Huddleston <jeremyhu apple com>
MFC after:	2 weeks

usr.bin/newgrp/newgrp.c

@@ -140,7 +140,7 @@ restoregrps(void)
 	if (initres < 0)
 		warn("initgroups");
 	if (setres < 0)
-		warn("setgroups");
+		warn("setgid");
 }
 
 static void
@@ -220,7 +220,7 @@ addgroup(const char *grpname)
 
 	/* Add old effective gid to supp. list if it does not exist. */
 	if (egid != grp->gr_gid && !inarray(egid, grps, ngrps)) {
-		if (ngrps == ngrps_max)
+		if (ngrps + 1 >= ngrps_max)
 			warnx("too many groups");
 		else {
 			grps[ngrps++] = egid;