dateutils: strptime for Python-2.4 compatibility

* Introduces a compatibility function called strptime which is
  equivalent to datetime.strptime so that it would work for
  both Python 2.4 and higher versions.

Reviewed-by: Tibor Simko <tibor.simko@cern.ch>
Merge branch 'maint-1.1'

* maint-1.1:
  dateutils: strptime for Python-2.4 compatibility