.to_excel() cuts off columns
Today I discovered a strange behavior: When I am writing a DataFrame with `.to_excel()`, it cuts columns. Compared with the same DataFrame with `.to_csv()` or `.head()`, you can see the difference, that the last 8 columns are missing.

You can reproduce this by downloading `Features.pkl` from [here](https://dl.dropboxusercontent.com/u/16985007/Features.pkl) and then:

``` python
import pandas as pd
df = pd.read_pickle('Features.pkl')
df.head() # see the last 8 columns!
df.to_excel('Features.xlsx', index=False, header=False)
# see the Excel, you do not have these last 8 columns
# in a .to_csv() you have them
```

Funny part: If you `df.ix[:,-71:].to_excel('Features.xlsx', index=False, header=False)` you have one of the missing columns. If you do `df.ix[:,-70:].to_excel('Features.xlsx', index=False, header=False)` you have two and so on...

``` python
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.10.final.0
python-bits: 64
OS: Darwin
OS-release: 14.5.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: de_DE.UTF-8

pandas: 0.16.2
nose: 1.3.7
Cython: 0.22.1
numpy: 1.9.2
scipy: 0.16.0
statsmodels: 0.6.1
IPython: 3.2.0
sphinx: 1.3.1
patsy: 0.3.0
dateutil: 2.4.2
pytz: 2015.4
bottleneck: 1.0.0
tables: 3.2.0
numexpr: 2.4.3
matplotlib: 1.4.3
openpyxl: 1.8.6
xlrd: 0.9.3
xlwt: 1.0.0
xlsxwriter: 0.7.3
lxml: 3.4.4
bs4: 4.3.2
html5lib: None
httplib2: 0.9
apiclient: None
sqlalchemy: 1.0.5
pymysql: None
psycopg2: None
```
