Add basic history api and implement it under gtk.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/SOC2011_WEBVIEW@68108 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/webview.h

@@ -199,6 +199,16 @@ public:
     */
     virtual void GoForward() = 0;
 
+    /**
+        Clear the history, this will also remove the visible page.
+    */
+    virtual void ClearHistory() = 0;
+    
+    /**
+        Enable or disable the history. This will also clear the history.
+    */
+    virtual void EnableHistory(bool enable = true) = 0;
+    
     /**
         Load a HTMl document (web page) from a URL
         @param url the URL where the HTML document to display can be found