Added the -G option to allow logins only for users that are members of a certain group. This allows finer control of an instance on who can and cannot login over a certain instance (e.g. password and not key). Needs double-checking and ensuring it meets platform requirements.

--- a/runopts.h	Mon Feb 19 23:04:46 2018 +0800
+++ b/runopts.h	Tue Feb 20 02:11:55 2018 +0000
@@ -92,6 +92,8 @@
 #endif
 
 	int norootlogin;
+        char *grouploginname;
+        gid_t *grouploginid;
 
 	int noauthpass;
 	int norootpass;