Add a wrapper for setgroups() that trims off extra groups and retries

if setgroups() fails.  Also add some missing addrefs for PERM_USER
and PERM_FULL_USER.

src/sudo.h

@@ -227,6 +227,9 @@ void aix_setauthdb(char *user);
 /* interfaces.c */
 int get_net_ifs(char **addrinfo);
 
+/* setgroups.c */
+int sudo_setgroups(int ngids, const GETGROUPS_T *gids);
+
 #ifndef errno
 extern int errno;
 #endif