When pasting, translate \n into \r. This matches xterm and putty's behaviour,

and makes emacs happy when pasting into some modes. A new -r (raw) flag to
paste-buffer pastes without the translation.

From Kalle Olavi Niemitalo, thanks!

tmux.h

@@ -858,6 +858,7 @@ struct cmd_entry {
 #define CMD_UFLAG 0x100
 #define CMD_BIGDFLAG 0x200
 #define CMD_BIGUFLAG 0x400
+#define CMD_RFLAG 0x800
 
 	int		 flags;