Add missing imports for posix.py for OS X
These don't seem to do harm on Linux.
--- a/mercurial/posix.py Fri Mar 27 13:39:18 2009 +0100
+++ b/mercurial/posix.py Fri Mar 27 17:56:18 2009 +0100
@@ -9,7 +9,7 @@
"""
from i18n import _
-import os, sys, osutil, errno, stat, getpass
+import os, sys, osutil, errno, stat, getpass, pwd, grp
posixfile = file
nulldev = '/dev/null'