be explicit about the actual location of the missing file

dep_util.py

@@ -19,7 +19,8 @@ def newer (source, target):
     Raise DistutilsFileError if 'source' does not exist.
     """
     if not os.path.exists(source):
-        raise DistutilsFileError, "file '%s' does not exist" % source
+        raise DistutilsFileError, ("file '%s' does not exist" %
+                                   os.path.abspath(source))
     if not os.path.exists(target):
         return 1