Add NewClaimWithTimestamp

Remedy #4

claim.go

@@ -16,8 +16,18 @@ type Claim struct {
 }
 
 // NewClaim claims ownership of a specified selection, and allows using data
-// passed to it to fulfill requests for the selection's contents.
+// passed to it to fulfill requests for the selection's contents. If the claim
+// happens because of a user input event, use NewClaimWithTimestamp instead of
+// this function. See the documentation of NewClaimWithTimestamp for details.
 func NewClaim (window *xwindow.Window, selection xproto.Atom, data Data) *Claim {
+	return NewClaimWithTimestamp(window, selection, data, 0)
+}
+
+// NewClaimWithTimestamp claims ownership of a specified selection, and allows
+// using data passed to it to fulfill requests for the selection's contents. The
+// timestamp should be set to that of the event that triggered the claim, such
+// as a Ctrl+C event, or a mouse motion that led to text being selected.
+func NewClaimWithTimestamp (window *xwindow.Window, selection xproto.Atom, data Data, timestamp xproto.Timestamp) *Claim {
 	// Follow:
 	// https://tronche.com/gui/x/icccm/sec-2.html#s-2.1
 	
@@ -35,7 +45,7 @@ func NewClaim (window *xwindow.Window, selection xproto.Atom, data Data) *Claim
 	// owner of the selection.
 	err := xproto.SetSelectionOwnerChecked (
 		window.X.Conn(),
-		window.Id, selection, 0).Check() // FIXME: should not be zero
+		window.Id, selection, timestamp).Check()
 	if err != nil { return nil }
 
 	ownerReply, err := xproto.GetSelectionOwner (