identity get_rate

[sposs]

It would be nice that the conversion from one currency to itself also work

>>> c.get_rate("CHF", "CHF")
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/home/user/.virtualenvs/tool/local/lib/python2.7/site-packages/forex_python/converter.py", line 67, in get_rate
    base_cur, dest_cur, date_str))
RatesNotAvailableError: Currency Rate CHF => CHF not available for Date latest