Fix a variable aliasing error.

gcl.py

Index: gcl.py
diff --git a/gcl.py b/gcl.py
index 3ee71de94ec468add1c5db6eca4956f95b7cf588..1a9ce9d4957b5bcf6e8c311b6d7b429dc257f14b 100755
--- a/gcl.py
+++ b/gcl.py
@@ -719,9 +719,10 @@ def GenerateDiff(files, root=None):
 
   diff = []
   for filename in files:
+    # TODO(maruel): Use SVN.DiffItem().
     # Use svn info output instead of os.path.isdir because the latter fails
     # when the file is deleted.
-    if SVN.CaptureInfo(file).get('Node Kind') == 'directory':
+    if SVN.CaptureInfo(filename).get('Node Kind') == 'directory':
       continue
     # If the user specified a custom diff command in their svn config file,
     # then it'll be used when we do svn diff, which we don't want to happen