Empty dataframe not equal to another empty dataframe in 0.16.1
I searched the issues list for "empty dataframe"  but did not find anything matching. 

In pandas 0.16.1, the result of adding 2 empty dataframes  is not equal to another empty dataframe. 

This code, in pandas 0.15.2, does what is expected: 

``` python
import pandas as pd

pd.show_versions()

df1 = pd.DataFrame()

df2 = pd.DataFrame()

assert df1.equals(df1)

assert df2.equals(df1)

assert (df1+df1).equals(df2)
```

It fails in 0.16.1.

0.15.2 output:

``` python

INSTALLED VERSIONS
------------------
commit: None
python: 2.7.7.final.0
python-bits: 64
OS: Windows
OS-release: 7
machine: AMD64
processor: Intel64 Family 6 Model 26 Stepping 5, GenuineIntel
byteorder: little
LC_ALL: None
LANG: en_GB

pandas: 0.15.2
nose: 1.3.6
Cython: 0.21.1
numpy: 1.9.2
scipy: 0.15.1
statsmodels: None
IPython: 3.1.0
sphinx: 1.3.1
patsy: 0.3.0
dateutil: 2.4.2
pytz: 2015.4
bottleneck: 0.8.0
tables: 3.1.1
numexpr: 2.3.1
matplotlib: 1.4.0
openpyxl: 1.8.5
xlrd: 0.9.3
xlwt: 0.7.5
xlsxwriter: 0.7.2
lxml: 3.4.0
bs4: 4.3.2
html5lib: 0.999
httplib2: None
apiclient: None
rpy2: None
sqlalchemy: 0.9.7
pymysql: None
psycopg2: None
```

0.16.1 output:

``` python
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.9.final.0
python-bits: 64
OS: Windows
OS-release: 7
machine: AMD64
processor: Intel64 Family 6 Model 26 Stepping 5, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None

pandas: 0.16.1
nose: 1.3.6
Cython: 0.22
numpy: 1.9.2
scipy: 0.14.0
statsmodels: 0.6.1
IPython: 3.1.0
sphinx: 1.3.1
patsy: 0.3.0
dateutil: 2.4.2
pytz: 2015.4
bottleneck: 0.8.0
tables: 3.1.1
numexpr: 2.3.1
matplotlib: 1.4.3
openpyxl: None
xlrd: 0.9.3
xlwt: None
xlsxwriter: 0.7.2
lxml: None
bs4: 4.3.2
html5lib: 0.999
httplib2: None
apiclient: None
sqlalchemy: 1.0.4
pymysql: None
psycopg2: None
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
c:\test_empty_add_0.16.1.py in <module>()
     11 assert df2.equals(df1)
     12
---> 13 assert (df1+df1).equals(df2)

AssertionError:
```
