Implementing "goBack", "goForward" and "go".

Completing work for [Issue #808](http://code.google.com/p/phantomjs/issues/detail?id=808).

src/webpage.cpp

@@ -45,6 +45,7 @@
 #include <QPainter>
 #include <QPrinter>
 #include <QWebHistory>
+#include <QWebHistoryItem>
 #include <QWebElement>
 #include <QWebFrame>
 #include <QWebPage>
@@ -425,10 +426,10 @@ bool WebPage::canGoBack()
     return m_customWebPage->history()->canGoBack();
 }
 
-bool WebPage::back()
+bool WebPage::goBack()
 {
     if (canGoBack()) {
-        m_customWebPage->triggerAction(QWebPage::Back);
+        m_customWebPage->history()->back();
         return true;
     }
     return false;
@@ -439,15 +440,32 @@ bool WebPage::canGoForward()
     return m_customWebPage->history()->canGoForward();
 }
 
-bool WebPage::forward()
+bool WebPage::goForward()
 {
     if (canGoForward()) {
-        m_customWebPage->triggerAction(QWebPage::Forward);
+        m_customWebPage->history()->forward();
         return true;
     }
     return false;
 }
 
+bool WebPage::go(int historyItemRelativeIndex)
+{
+    // Convert the relative index to absolute
+    int historyItemIndex = m_customWebPage->history()->currentItemIndex() + historyItemRelativeIndex;
+
+    // Fetch the right item from the history
+    QWebHistoryItem historyItem = m_customWebPage->history()->itemAt(historyItemIndex);
+
+    // Go to the history item, if it's valid
+    if (historyItem.isValid()) {
+        m_customWebPage->history()->goToItem(historyItem);
+        return true;
+    }
+
+    return false;
+}
+
 void WebPage::reload()
 {
     m_customWebPage->triggerAction(QWebPage::Reload);

src/webpage.h

@@ -412,10 +412,10 @@ public slots:
     bool canGoBack();
     /**
      * Goes back in the Navigation History
-     * @brief back
+     * @brief goBack
      * @return "true" if it does go back in the Navigation History, "false" otherwise
      */
-    bool back();
+    bool goBack();
     /**
      * Checks if this Page can go forward in the Navigation History (i.e. next URL)
      * @brief canGoForward
@@ -424,10 +424,21 @@ public slots:
     bool canGoForward();
     /**
      * Goes forward in the Navigation History
-     * @brief forward
+     * @brief goForward
      * @return "true" if it does go forward in the Navigation History, "false" otherwise
      */
-    bool forward();
+    bool goForward();
+    /**
+     * Go to the page identified by its relative location to the current page.
+     * For example '-1' for the previous page or 1 for the next page.
+     *
+     * Modelled after JavaScript "window.go(num)" method:
+     * {@see https://developer.mozilla.org/en-US/docs/DOM/window.history#Syntax}.
+     * @brief go
+     * @param historyRelativeIndex
+     * @return "true" if it does go forward/backgward in the Navigation History, "false" otherwise
+     */
+    bool go(int historyRelativeIndex);
     /**
      * Reload current page
      * @brief reload