Add the necessary default settings to enable HTML output in the Jupyter

Notebook pager for the IPython shell.

We need to replace the monkeypatching of getdoc -> sage_getdoc with
getdoc -> sage_getdoc_original.  The difference is that the former also
runs sage.misc.sagedoc.format() over the docstring, whereas the latter
doesn't.  This is necessary so that by the time the docstring reaches
sphinxify_mimebundle() it hasn't been re-formatted yet.

That said, it's still not entirely clear how this change will affect
other functionality, as getdoc is used in several places by
IPython.core.oinspect.

We also need to inject our sphinxify_mimebundle() in place of the
default sphinxify in IPython.core.interactiveshell.  Unfortunate but not
easily avoidable at the moment.

src/sage/repl/ipython_extension.py

@@ -437,6 +437,10 @@ def __init__(self, shell=None):
 
         self.register_interface_magics()
 
+        # Change some default settings to allow displaying HTML help
+        self.shell.enable_html_pager = True
+        self.shell.sphinxify_docstring = True
+
         if SAGE_IMPORTALL == 'yes':
             self.init_environment()
 
@@ -497,11 +501,18 @@ def init_inspector(self):
         # the global :class:`IPython.core.oinspect` module namespace.
         # Thus, we have to monkey-patch.
         import IPython.core.oinspect
-        IPython.core.oinspect.getdoc = LazyImport("sage.misc.sageinspect", "sage_getdoc")
+        IPython.core.oinspect.getdoc = \
+            LazyImport("sage.misc.sageinspect", "sage_getdoc_original")
         IPython.core.oinspect.getsource = LazyImport("sage.misc.sagedoc", "my_getsource")
         IPython.core.oinspect.find_file = LazyImport("sage.misc.sageinspect", "sage_getfile")
         IPython.core.oinspect.getargspec = LazyImport("sage.misc.sageinspect", "sage_getargspec")
 
+        # Similarly to enable Sage's sphinxify we must use a similar hack, but
+        # on IPython.core.interactiveshell
+        import IPython.core.interactiveshell
+        IPython.core.interactiveshell.sphinxify = \
+            LazyImport("sage.misc.sphinxify", "sphinxify_mimebundle")
+
     def init_line_transforms(self):
         """
         Set up transforms (like the preparser).