Fixed QwtPlot.setAxisAutoScale/setAutoReplot args

Added missing default state argument (boolean=True) to QwtPlot's setAxisAutoScale and setAutoReplot methods,
in order to fit Qwt C++ library original method signatures (see http://qwt.sourceforge.net/class_qwt_plot.html#ab1cbce6d43ff9772735a9df9104f882f)

Author: PierreRaybaut

qwt/plot.py

@@ -646,7 +646,7 @@ def setAxisFont(self, axisId, font):
         if self.axisValid(axisId):
             return self.axisWidget(axisId).setFont(font)
 
-    def setAxisAutoScale(self, axisId, on):
+    def setAxisAutoScale(self, axisId, on=True):
         """
         Enable autoscaling for a specified axis
 
@@ -947,7 +947,7 @@ def autoRefresh(self):
         if self.__data.autoReplot:
             self.replot()
 
-    def setAutoReplot(self, tf):
+    def setAutoReplot(self, tf=True):
         """
         Set or reset the autoReplot option