replacement of the "install" command so that installation is always via
easy_install, but doesn't use the previous kludgy intereception technique.
Allow ``extra_path`` to be set, but ignore it, so that when easy_install
wraps a package that uses it, there won't be any confusion as to the
desired installation location.

--HG--
branch : setuptools
extra : convert_revision : svn%3A6015fed2-1504-0410-9fe1-9d1591cc4771/sandbox/trunk/setuptools%4041181