fillna() is incomplete after performing resample()
#### Code Sample

Make data

```
>>> dates = pd.date_range('01-01-2015','01-07-2015', freq='B')
>>> df = pd.DataFrame({'a':[1,2,np.nan,4,5],'b':[6,7,8,9,np.nan]}, dates)
>>> print(df)
              a    b
2015-01-01  1.0  6.0
2015-01-02  2.0  7.0
2015-01-05  NaN  8.0
2015-01-06  4.0  9.0
2015-01-07  5.0  NaN
```

Then re-sample

```
>>> df = df.resample('D').fillna(method='ffill')
>>> print(df)
              a    b
2015-01-01  1.0  6.0
2015-01-02  2.0  7.0
2015-01-03  2.0  7.0
2015-01-04  2.0  7.0
2015-01-05  NaN  8.0
2015-01-06  4.0  9.0
2015-01-07  5.0  NaN
```
#### Expected Output

`fillna()` should have filled all of the `NaNs`, but instead it seems to miss those that existed before `resample()` was called.
#### output of `pd.show_versions()`

```
INSTALLED VERSIONS
------------------
commit: None
python: 3.4.3.final.0
python-bits: 64
OS: Windows
OS-release: 7
machine: AMD64
processor: Intel64 Family 6 Model 15 Stepping 11, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None

pandas: 0.18.1
nose: None
pip: 8.1.2
setuptools: 22.0.5
Cython: 0.23.1
numpy: 1.11.0
scipy: 0.17.1
statsmodels: 0.6.1
xarray: None
IPython: 3.2.1
sphinx: None
patsy: 0.3.0
dateutil: 2.5.3
pytz: 2016.4
blosc: None
bottleneck: None
tables: 3.2.0
numexpr: 2.4.3
matplotlib: 1.4.2
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 0.9999999
httplib2: None
apiclient: None
sqlalchemy: 1.0.13
pymysql: None
psycopg2: None
jinja2: 2.7.3
boto: None
pandas_datareader: None
```
