New command, if-shell (alias if). Executes the tmux command in the second

argument if the shell command in the first succeeds, for example:

       if "[ -e ~/.tmux.conf.alt ]" "source .tmux.conf.alt"

Written by Tiago Cunha, many thanks.

cmd.c

@@ -42,6 +42,7 @@ const struct cmd_entry *cmd_table[] = {
 	&cmd_down_pane_entry,
 	&cmd_find_window_entry,
 	&cmd_has_session_entry,
+	&cmd_if_shell_entry,
 	&cmd_kill_pane_entry,
 	&cmd_kill_server_entry,
 	&cmd_kill_session_entry,