Make rmagic display call compatible with updated API

Passing all arguments as keywords will work with the previous API as
well.

CC @davclark - You'll want to copy this change across to rpy2, because
without it, rmagic is broken with IPython master.

IPython/extensions/rmagic.py

@@ -665,7 +665,7 b' class RMagics(Magics):'
                 self.shell.push({output:self.Rconverter(self.r(output), dataframe=True)})
 
         for tag, disp_d in display_data:
-            publish_display_data(tag, disp_d)
+            publish_display_data(data=disp_d, source=tag)
 
         # this will keep a reference to the display_data
         # which might be useful to other objects who happen to use