Excel corrupted file when using to_csv method
#### Input data

[foo1.csv](https://www.dropbox.com/s/peojg2ugn6m4dtt/foo1.csv?dl=0)
#### Code Sample, a copy-pastable example if possible

import pandas as pd
df = pd.read_csv('foo1.csv', sep='\t', encoding='utf-16le', engine='python')
df.to_csv("out.csv", mode='wb', sep='\t', encoding='utf-16le', engine='python')
#### Expected Output

out.csv should be exactly the same than foo1.csv, instead it becomes "corrupted". For example, trying to open it with excel will show a message saying the file is corrupted and it cannot be opened. Checking the output with an hex editor you can see some extra bytes have been added into the header of out.csv as well as other additional bytes.
#### output of `pd.show_versions()`

commit: None
python: 2.7.10.final.0
python-bits: 64
OS: Windows
OS-release: 7
machine: AMD64
processor: Intel64 Family 6 Model 60 Stepping 3, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None

pandas: 0.18.0
nose: None
pip: 8.1.1
setuptools: 20.10.1
Cython: None
numpy: 1.10.4
scipy: 0.17.0
statsmodels: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.4.2
pytz: 2015.7
blosc: None
bottleneck: None
tables: None
numexpr: None
matplotlib: 1.5.0
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: 4.4.1
html5lib: 0.9999999
httplib2: 0.9.2
apiclient: None
sqlalchemy: 1.0.12
pymysql: None
psycopg2: None
jinja2: 2.8
boto: None
