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``.