Lots of work on the display system, focused on pylab stuff.

* Moved the pprint attribute to PlainTextFormatter.
* Added DisplayFormatter.plain_text_only for disabling all but the
  plain text formatting. This is now used by doctest_mode.
* Remove result_display hook.
* Fixed doctest_mode magic.
* Refactored inline matplotlib backend to use new display system.
* Added display formatter for matplotlib.figure.Figure objects.
  so the display system will show the svg for them.
* Added display and display_png to the user's namespace in pylab.
* Cleaned up pylabtools.py

setupbase.py

@@ -213,13 +213,7 @@ def find_data_files():
     data_files = [ (manpagebase, manpages),
                    (pjoin(docdirbase, 'extensions'), igridhelpfiles),
                    ] + manual_files + example_files
-                 
-    ## import pprint  # dbg
-    ## print('*'*80)
-    ## print('data files')
-    ## pprint.pprint(data_files)
-    ## print('*'*80)
-    
+
     return data_files