Fix issue with one file diff shim

Author: danvk

webdiff/argparser.py

@@ -80,10 +80,8 @@ def parse(args):
 # TODO: move into dirdiff?
 def _shim_for_file_diff(a_file, b_file):
     '''Sets A_DIR, B_DIR and DIFF to do a one-file diff.'''
-    dirname = os.path.dirname
-    basename = os.path.basename
-    return LocalFileDiff(dirname(a_file), basename(a_file),
-                         dirname(b_file), basename(b_file),
+    return LocalFileDiff(os.path.dirname(a_file), a_file,
+                         os.path.dirname(b_file), b_file,
                          False)  # probably not a move