Fixed the followin bugs

- In amsn2/ui/front_ends_qt4/login.py change the name of function signin_to_accoun_aa to signin_to_account
- In amsn2/backend/defaultaccountbackend.py added one line using the str function to convert the email variable to a python string.
  This fix the error to use qt4 front end: AttributeError: 'QString' object has no attribute 'lower'

amsn2/backend/defaultaccountbackend.py

@@ -186,4 +186,5 @@ def get_file_location_DP(self, email, uid, shac):
         return os.path.join(dir, shac.encode("hex")+".img")
 
     def _get_dir(self, email):
+	email = str(email)
         return email.lower().strip().replace("@","_at_")

amsn2/ui/front_ends/qt4/login.py

@@ -143,7 +143,7 @@ def __login_clicked(self):
         accv.save_password = self.ui.checkRememberPass.isChecked()
         accv.autologin = self.ui.checkSignInAuto.isChecked()
 
-        self._amsn_core.signin_to_accoun_aa(self, accv)
+        self._amsn_core.signin_to_account(self, accv)
 
     def signout(self):
         pass