BUG: concat of same-tz needs string comparison for uniqueness

Author: jreback

ci/requirements-3.4.run

@@ -1,4 +1,4 @@
-pytz
+pytz=2015.7
 numpy=1.8.1
 openpyxl
 xlsxwriter

pandas/types/concat.py

@@ -249,7 +249,7 @@ def convert_to_pydatetime(x, axis):
             # thus no need to care
 
             # we require ALL of the same tz for datetimetz
-            tzs = set([x.tz for x in to_concat])
+            tzs = set([str(x.tz) for x in to_concat])
             if len(tzs) == 1:
                 from pandas.tseries.index import DatetimeIndex
                 new_values = np.concatenate([x.tz_localize(None).asi8