Bring back file upload support.

Instead of using command-line option, file can be uploaded using
WebPage.uploadFile function, e.g.:

  var page = new WebPage();
  page.open(....., function () {
      page.uploadFile('input#attachment', '/path/to/file');
  });

uploadFile() accepts selector name (first argument), this is used to identify
which input element will need the filename (second argument).

python/webpage.py

@@ -42,8 +42,13 @@ class CustomPage(QWebPage):
         self.parent = parent
         self.m_userAgent = QWebPage.userAgentForUrl(self, QUrl())
 
+        self.m_uploadFile = ''
+
         do_action('CustomPageInit', Bunch(locals()))
 
+    def chooseFile(self, originatingFrame, oldFile):
+        return self.m_uploadFile
+
     def shouldInterruptJavaScript(self):
         QApplication.processEvents(QEventLoop.AllEvents, 42)
         return False
@@ -327,6 +332,21 @@ class WebPage(QObject):
 
         return image.save(fileName)
 
+    @pyqtSlot(str, str)
+    def uploadFile(self, selector, fileName):
+        el = self.m_mainFrame.findFirstElement(selector)
+        if el.isNull():
+            return
+
+        self.m_webPage.m_uploadFile = fileName
+        el.evaluateJavaScript('''
+            (function (el) {
+                var ev = document.createEvent('MouseEvents');
+                ev.initEvent('click', true, true);
+                el.dispatchEvent(ev);
+            })(this)
+        ''')
+
     @pyqtProperty('QVariantMap')
     def viewportSize(self):
         size = self.m_webPage.viewportSize()