When in window filtering mode, reset filter before showing window

When we had a filtered set of windows, and want to exit the overview
into a particular window, what we do is re-show all the old windows
first, but don't reset the scaling on them.  This will involve
some overlapping, but that's not a big deal because we'll immediately
get overlap anyways in the normal case zooming the windows back.

https://bugzilla.gnome.org/show_bug.cgi?id=594699

js/ui/overview.js

@@ -342,7 +342,7 @@ Overview.prototype = {
         this.emit('showing');
     },
 
-    hide : function() {
+    hide: function() {
         if (!this.visible || this._hideInProgress)
             return;
 
@@ -410,7 +410,6 @@ Overview.prototype = {
      */
     activateWindow: function (metaWindow, time) {
          this._workspaces.activateWindowFromOverview(metaWindow, time);
-         this.hide();
     },
 
     //// Private methods ////