API: Wrong DateOffset behaviour with DST changes
Given a timezone-aware Timestamp:

    foo = pd.Timestamp('2016-10-30 00:00:00', tz=pytz.timezone('Europe/Helsinki'))

(Please note that `2016-10-30` is a 25-hour day, due to a DST change. This day the hour changes from `+0300` to `+0200`)

I'm trying to get the next day. If I understand correctly the DateOffset behaviour, all these lines should be equivalent:

    foo + pd.tseries.frequencies.to_offset('D')
    foo + pd.tseries.offsets.Day()
    foo + pd.DateOffset()
    foo + pd.DateOffset(1)
    foo + pd.DateOffset(days=1)

But the first four return a wrong date, presumably because they're not adding a day, but 24 hours:

    Timestamp('2016-10-30 23:00:00+0200', tz='Europe/Helsinki')

And for some reason, the last one returns the correct date:

    Timestamp('2016-10-31 00:00:00+0200', tz='Europe/Helsinki')

#### Output of ``pd.show_versions()``

<details>
>>> pd.show_versions()

INSTALLED VERSIONS
------------------
commit: None
python: 3.4.6.final.0
python-bits: 64
OS: Darwin
OS-release: 16.6.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: es_ES.UTF-8
LOCALE: es_ES.UTF-8

pandas: 0.20.3
pytest: None
pip: 9.0.1
setuptools: 28.8.0
Cython: None
numpy: 1.13.1
scipy: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.6.1
pytz: 2017.2
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: None
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: None
s3fs: None
pandas_gbq: None
pandas_datareader: None
</details>