Add --no-ewmh-fullscreen

This arg reverts to the old behaviour of checking for fullscreen
windows.

src/config_libconfig.c

@@ -355,6 +355,8 @@ char *parse_config_libconfig(options_t *opt, const char *config_file, bool *shad
 	lcfg_lookup_bool(&cfg, "detect-transient", &opt->detect_transient);
 	// --detect-client-leader
 	lcfg_lookup_bool(&cfg, "detect-client-leader", &opt->detect_client_leader);
+	// --no-ewmh-fullscreen
+	lcfg_lookup_bool(&cfg, "no-ewmh-fullscreen", &opt->no_ewmh_fullscreen);
 	// --shadow-exclude
 	parse_cfg_condlst(&cfg, &opt->shadow_blacklist, "shadow-exclude");
 	// --fade-exclude