Update the URL used to fetch 'ez_setup.py'

Use the official, non-version-pinned version.

CHANGES.rst

 Change History
 **************
 
+Unreleased
+==========
+
+- Updated the URL used to fetch ``ez_setup.py`` to the official, non-version-
+  pinned version.
+
 2.2.0 (2013-07-05)
 ==================
 

bootstrap/bootstrap.py

@@ -75,8 +75,8 @@ except ImportError:
     except ImportError:
         from urllib2 import urlopen
 
-    # XXX use a more permanent ez_setup.py URL when available.
-    exec(urlopen('https://bitbucket.org/pypa/setuptools/raw/0.7.2/ez_setup.py'
+    exec(urlopen(
+            'https://bitbucket.org/pypa/setuptools/raw/bootstrap/ez_setup.py'
                 ).read(), ez)
     setup_args = dict(to_dir=tmpeggs, download_delay=0)
     ez['use_setuptools'](**setup_args)