It seems silly to use progname for version, just always say tmux.

tmux.c

@@ -401,7 +401,7 @@ main(int argc, char **argv)
 			cfg_quiet = 0;
 			break;
  		case 'V':
-			printf("%s %s\n", getprogname(), getversion());
+			printf("tmux %s\n", getversion());
  			exit(0);
 		case 'l':
 			flags |= CLIENT_LOGIN;