Merge pull request #384 from FMassin/patch-1

Transparency support

Author: WeatherGod

lib/mpl_toolkits/basemap/__init__.py

@@ -4243,6 +4243,7 @@ def arcgisimage(self,server='http://server.arcgisonline.com/ArcGIS',\
 size=%s,%s&\
 dpi=%s&\
 format=png32&\
+transparent=true&\
 f=image" %\
 (server,service,xmin,ymin,xmax,ymax,self.epsg,self.epsg,xpixels,ypixels,dpi)
         # print URL?