Merge pull request pandas-dev#25 from manahl/bugfix/TS-225-tickstore-python-write-gives

TS-225 Fixed a warning: don't log if the datetime already has a timezone

Author: jamesblackburn

arctic/tickstore/tickstore.py

@@ -496,7 +496,8 @@ def _to_buckets(self, x, symbol):
 
     def _to_ms(self, date):
         if isinstance(date, dt):
-            logger.warn('WARNING: treating naive datetime as London in write path')
+            if not date.tzinfo:
+                logger.warn('WARNING: treating naive datetime as London in write path')
             return datetime_to_ms(date)
         return date