Add some const and fix a warning.

cmd-new-window.c

@@ -44,7 +44,8 @@ cmd_new_window_exec(struct cmd *self, struct cmd_ctx *ctx)
 	struct args	*args = self->args;
 	struct session	*s;
 	struct winlink	*wl;
-	char		*cmd, *cwd, *cause;
+	const char     	*cmd, *cwd;
+	char		*cause;
 	int		 idx, last, detached;
 
 	if (args_has(args, 'a')) {

cmd-split-window.c

@@ -58,8 +58,8 @@ cmd_split_window_exec(struct cmd *self, struct cmd_ctx *ctx)
 	struct window		*w;
 	struct window_pane	*wp, *new_wp = NULL;
 	struct environ		 env;
-	char		 	*cmd, *cwd, *cause, *new_cause;
-	const char		*shell;
+	const char	       	*cmd, *cwd, *shell;
+	char			*cause, *new_cause;
 	u_int			 hlimit, paneidx;
 	int			 size, percentage;
 	enum layout_type	 type;

cmd.c

@@ -1215,10 +1215,10 @@ cmd_template_replace(char *template, const char *s, int idx)
 }
 
 /* Return the default path for a new pane. */
-char *
+const char *
 cmd_get_default_path(struct cmd_ctx *ctx)
 {
-	char			*cwd;
+	const char		*cwd;
 	struct session		*s;
 	struct window_pane	*wp;
 	struct environ_entry	*envent;

tmux.h

@@ -1565,7 +1565,7 @@ int		 cmd_find_index(
 struct winlink	*cmd_find_pane(struct cmd_ctx *,
 		     const char *, struct session **, struct window_pane **);
 char		*cmd_template_replace(char *, const char *, int);
-char		*cmd_get_default_path(struct cmd_ctx *ctx);
+const char     	*cmd_get_default_path(struct cmd_ctx *ctx);
 extern const struct cmd_entry *cmd_table[];
 extern const struct cmd_entry cmd_attach_session_entry;
 extern const struct cmd_entry cmd_bind_key_entry;