added argparse for python version <2.7

setup.py

@@ -58,6 +58,7 b' if sys.version_info < (2, 6):'
 
 if sys.version_info < (2, 7):
     requirements.append("unittest2")
+    requirements.append("argparse")
 
 if is_windows:
     requirements.append("mercurial==2.4.2")