Convert dict values to string for Python 2 support

As @jensens pointed out in a comment about issue pypa#1136 this is a first step to prevent the occurrence of that issue

setuptools/config.py

@@ -226,7 +226,7 @@ def _parse_dict(cls, value):
             if sep != separator:
                 raise DistutilsOptionError(
                     'Unable to parse option value to dict: %s' % value)
-            result[key.strip()] = val.strip()
+            result[key.strip()] = str(val.strip())
 
         return result