Fix histocurve rendering

The x axis used a range of numbers and dates: numbers of the points and
dates for the axis range. This prevented the histocurve from being
rendered.

This changes the graph to use only numbers, but adds a formatter so that
they're still shown as dates. This allows the graph to be rendered
correctly again.

graphs.py

@@ -716,7 +716,12 @@ def create_stackedareacurve(self, width, dpi, filename):
 		#ax[0].autoscale(enable=True, axis='x', tight=True)
 		ax[0].set_ylim(bottom=0, top=ymax)
 		#ax[0].set_xlim(left=dates[0], right=dates[len(dates) - 1])
-		ax[0].set_xlim(self.start_date, self.end_date)
+		ax[0].set_xlim(self.start_date.toordinal(), self.end_date.toordinal())
+
+		# Display the x axis labels as dates rather than numbers
+		def formatter(x, pos):
+			return datetime.date.fromordinal(int(x))
+		ax[0].xaxis.set_major_formatter(formatter)
 
 		# Averages
 		duration = self.dates[len(self.dates) - 1].toordinal() - self.dates[0].toordinal()