Add a get-clipboard option which when enabled (the default is off) uses

the same mechanism as palette requests to request clipboard from the
terminal and forward to the requesting pane. Remove the now-redundant
forward-to-pane ability from "refresh-client -l". GitHub issue 4275.

tmux.1

@@ -1361,12 +1361,11 @@ and sets an environment variable for the newly created session; it may be
 specified multiple times.
 .Tg refresh
 .It Xo Ic refresh-client
-.Op Fl cDLRSU
+.Op Fl cDlLRSU
 .Op Fl A Ar pane:state
 .Op Fl B Ar name:what:format
 .Op Fl C Ar size
 .Op Fl f Ar flags
-.Op Fl l Op Ar target-pane
 .Op Fl r Ar pane:report
 .Op Fl t Ar target-client
 .Op Ar adjustment
@@ -1487,11 +1486,7 @@ a colon, then a report escape sequence.
 .Fl l
 requests the clipboard from the client using the
 .Xr xterm 1
-escape sequence.
-If
-.Ar target-pane
-is given, the clipboard is sent (in encoded form), otherwise it is stored in a
-new paste buffer.
+escape sequence and stores it in a new paste buffer.
 .Pp
 .Fl L ,
 .Fl R ,
@@ -4239,6 +4234,32 @@ passed through to applications running in
 .Nm .
 Attached clients should be detached and attached again after changing this
 option.
+.It Xo Ic get-clipboard
+.Op Ic both | request | buffer | off
+.Xc
+Controls the behaviour when an application requests the clipboard from
+.Nm .
+.Pp
+If
+.Ic off ,
+the request is ignored;
+if
+.Ic buffer ,
+.Nm
+responds with the newest paste buffer;
+.Ic request
+causes
+.Nm
+to request the clipboard from the most recently used client (if possible) and
+send the reply (if any) back to the application;
+.Ic buffer
+is the same as
+.Ic request
+but also creates a paste buffer.
+.Pp
+See also the
+.Ic set-clipboard
+option.
 .It Ic history-file Ar path
 If not empty, a file to which
 .Nm