keyword: use util.realpath instead of os.path.realpath stable

keyword: use util.realpath instead of os.path.realpath

This makes test-keyword.t pass on Python 2.4.1 (e.g. Debian sarge)

--- a/hgext/keyword.py	Mon Oct 24 13:32:23 2011 +0200
+++ b/hgext/keyword.py	Mon Oct 24 13:54:59 2011 +0200
@@ -86,7 +86,7 @@
 from mercurial import scmutil
 from mercurial.hgweb import webcommands
 from mercurial.i18n import _
-import os, re, shutil, tempfile
+import re, shutil, tempfile
 
 commands.optionalrepo += ' kwdemo'
 
@@ -647,7 +647,7 @@
             source = repo.dirstate.copied(dest)
             if 'l' in wctx.flags(source):
                 source = scmutil.canonpath(repo.root, cwd,
-                                           os.path.realpath(source))
+                                           util.realpath(source))
             return kwt.match(source)
 
         candidates = [f for f in repo.dirstate.copies() if