Merging the new-extensions branch....
Merging the new-extensions branch.
* Previously, the latex Sphinx docs were in a single chapter. This has been
fixed by adding a sixth argument of True to the ``latex_documents``
attribute of :file:`conf.py`.
* The ``psum`` example in the MPI documentation has been updated to mpi4py
version 1.1.0. Thanks to J. Thomas for this fix.
* The top-level, zero-install :file:`ipython.py` script has been updated to
the new application launching API.
* The extension loading functions have been renamed to
:func:`load_ipython_extension` and :func:`unload_ipython_extension`.
* The :mod:`IPython.extensions.pretty` extension has been moved out of
quarantine and fully updated to the new extension API.
* New magics for loading/unloading/reloading extensions have been added:
``%load_ext``, ``%unload_ext`` and ``%reload_ext``.
