Use Python's own JSON module for more robust unit testing. Alternative JSON...

Use Python's own JSON module for more robust unit testing. Alternative JSON modules may be faster but may also deliver slightly different output concerning whitespaces.

core/tests/test_pm3argparse.py

@@ -5,10 +5,7 @@ Testing our own little argument parser.
 import unittest
 import tempfile
 import gzip
-try:
-    import ujson as json
-except ImportError:
-    import json
+import json
 import ost
 from promod3.core import pm3argparse