Remove the namespace_packages option from the setup.py script

Why do this?  For some reason, if it's included, then the __init__.py for the
tracext package doesn't get installed.  There's probably a better way to do
this, but this will work for now.

diff -r 3ba729841466 setup.py
--- a/setup.py	Sun Jul 20 15:52:22 2008 -0600
+++ b/setup.py	Sun Jul 20 15:54:50 2008 -0600
@@ -19,6 +19,5 @@
       
       See %s for more details.
       """ % TracMercurial,
-      namespace_packages=['tracext'],
       packages=['tracext', 'tracext.hg'],
       entry_points={'trac.plugins': 'hg = tracext.hg.backend'})
