Fix click suppression after dragend in cases where click doesn't fire.

Fixes Issue #1005 for both behavior.zoom and behavior.drag

src/behavior/drag.js

@@ -65,18 +65,12 @@ d3.behavior.drag = function() {
       // if moved, prevent the mouseup (and possibly click) from propagating
       if (moved) {
         d3_eventCancel();
-        if (d3.event.target === eventTarget) w.on("click.drag", click, true);
+        if (d3.event.target === eventTarget) d3_eventSuppress('click');
       }
 
       w .on(touchId != null ? "touchmove.drag-" + touchId : "mousemove.drag", null)
         .on(touchId != null ? "touchend.drag-" + touchId : "mouseup.drag", null);
     }
-
-    // prevent the subsequent click from propagating (e.g., for anchors)
-    function click() {
-      d3_eventCancel();
-      w.on("click.drag", null);
-    }
   }
 
   drag.origin = function(x) {

src/behavior/zoom.js

@@ -115,12 +115,7 @@ d3.behavior.zoom = function() {
     function mouseup() {
       if (moved) d3_eventCancel();
       w.on("mousemove.zoom", null).on("mouseup.zoom", null);
-      if (moved && d3.event.target === eventTarget) w.on("click.zoom", click, true);
-    }
-
-    function click() {
-      d3_eventCancel();
-      w.on("click.zoom", null);
+      if (moved && d3.event.target === eventTarget) d3_eventSuppress('click');
     }
   }
 

src/event/event.js

@@ -13,6 +13,22 @@ function d3_eventSource() {
   return e;
 }
 
+// In some cases, e.g. on dragend of behavior.zoom and behavior.drag, we need
+// to suppress an event that fires immediately.
+function d3_eventSuppress(name) {
+  var w = d3.select(d3_window);
+  function unbind() {
+    w.on(name + ".suppress", null);
+  }
+  w.on(name + ".suppress", function() {
+    // prevent the subsequent event from propagating (e.g., for anchors)
+    d3_eventCancel();
+    unbind();
+  }, true);
+  // clear the handler after a 0ms timeout in case it doesn't fire after all
+  setTimeout(unbind, 0);
+}
+
 // Like d3.dispatch, but for custom events abstracting native UI events. These
 // events have a target component (such as a brush), a target element (such as
 // the svg:g element containing the brush) and the standard arguments `d` (the