BUG: edge case when reading from postgresl with read_sql_query and datetime with tz and chunksize
- When we don't specifiy a chunksize we get an object dtype which is ok
- We create a propery datetime64[ns, tz] type, but its a pytz.FixedOffset(....)
  which ATM is not really a useful/palatable type and is mostly confusing for now.
  In the future could attempt to coerce this to a nice tz, e.g. US/Eastern, ,not sure if
  this is possible. 
- Note that this is w/o parse_dates specified
