Fix doc build to eliminate matplotlib dependency.

docs/source/conf.py

@@ -36,8 +36,9 b" execfile('../../IPython/Release.py',iprelease)"
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
 extensions = ['sphinx.ext.autodoc',
-              'inheritance_diagram', 'only_directives', 'plot_directive',
+              'inheritance_diagram', 'only_directives',
               'ipython_console_highlighting', 
+              # 'plot_directive', # disabled for now, needs matplotlib
               ]
 
 # Add any paths that contain templates here, relative to this directory.