resample precision issue
#### Code Sample, a copy-pastable example if possible

```python
"""Bug pandas."""
from pandas import read_csv, to_datetime

try:
    from StringIO import StringIO
except ImportError:
    from io import StringIO

dtf = read_csv(StringIO('Time, Value\n'
                        '2017-11-08 15:14:04.421,1\n'
                        '2017-11-08 15:14:05.528,2\n'
                        '2017-11-08 15:14:06.714,3\n'
                        '2017-11-08 15:14:07.113,4\n'
                        '2017-11-08 15:14:08.282,5\n'
                        '2017-11-08 15:14:08.681,6\n'
                        '2017-11-08 15:14:10.650,7\n'
                        '2017-11-08 15:14:11.826,8\n'
                        '2017-11-08 15:14:12.225,9\n'
                        '2017-11-08 15:14:13.416,10'))

dtf.Time = to_datetime(dtf.Time)
dtf.set_index('Time', inplace=True)
print(dtf)
dtf2 = dtf.resample('1s').bfill(limit=1)
print(dtf2)
```
#### Problem description

Current output:
```
                      Value
Time                       
2017-11-08 15:14:04     1.0
2017-11-08 15:14:05     2.0
2017-11-08 15:14:06     3.0
2017-11-08 15:14:07     4.0
2017-11-08 15:14:08     5.0
2017-11-08 15:14:09     NaN
2017-11-08 15:14:10     7.0
2017-11-08 15:14:11     8.0
2017-11-08 15:14:12     9.0
2017-11-08 15:14:13    10.0
```

Main issue: `NaN` is not expected.

Secondary minor issue:
`bfill` with `limit` is changing type of the column, `bfill` without `limit` is not changing the dtype

#### Expected Output

```
                      Value
Time                       
2017-11-08 15:14:04     1
2017-11-08 15:14:05     2
2017-11-08 15:14:06     3
2017-11-08 15:14:07     4
2017-11-08 15:14:08     5
2017-11-08 15:14:09     6
2017-11-08 15:14:10     7
2017-11-08 15:14:11     8
2017-11-08 15:14:12     9
2017-11-08 15:14:13    10
```

#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 2.7.13.final.0
python-bits: 64
OS: Darwin
OS-release: 17.3.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.22.0
pytest: None
pip: 9.0.1
setuptools: 34.3.0
Cython: None
numpy: 1.14.0
scipy: None
pyarrow: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.6.1
pytz: 2017.3
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: None
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.9.5
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None
None

</details>