BUG: Period and Series/Index comparison raises TypeError
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry
  `Period` and `Series/Index` comparison raises `TypeError` if `Period` is on left hand side.

```
# OK
pd.Series([pd.Period('2011-01-01', freq='D')]) > pd.Period('2011-01-01', freq='D')
#0    False
# dtype: bool

# NG
pd.Period('2011-01-01', freq='D') > pd.Series([pd.Period('2011-01-01', freq='D')])
# TypeError: Cannot compare type 'Period' with type 'Series'
```

lgtm. merge on green (or you can ping and i can).
 thanks!
