BUG: Series.fillna(False) return 0.0(float) instead of bool
#### Code Sample, a copy-pastable example if possible

```
import pandas as pd
s1 = pd.Series([np.nan, np.nan, np.nan])
print s1.fillna(False)
```
#### Expected Output

```
0    False
1    False
2    False
dtype: bool
```

but the output is:

```
0    0.0
1    0.0
2    0.0
dtype: float64
```
#### output of `pd.show_versions()`

```
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.6.final.0
python-bits: 64
OS: Linux
OS-release: 3.13.0-30-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.18.0
nose: 1.3.1
pip: 8.1.1
setuptools: 20.3.1
Cython: None
numpy: 1.11.0
scipy: 0.13.3
statsmodels: 0.5.0
xarray: None
IPython: 4.2.0
sphinx: None
patsy: 0.2.1
dateutil: 2.5.3
pytz: 2016.4
blosc: None
bottleneck: None
tables: 3.1.1
numexpr: 2.2.2
matplotlib: 1.3.1
openpyxl: 1.7.0
xlrd: 0.9.2
xlwt: 0.7.5
xlsxwriter: None
lxml: None
bs4: 4.4.1
html5lib: 0.999
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: 0.7.2.None
psycopg2: None
jinja2: None
boto: 2.40.0


```
