to_json float precision bug
xref #15864 for more tests


#### Code Sample, a copy-pastable example if possible

```python
>>> pd.DataFrame([dict(a_float=0.99999999999999944)]).to_json(double_precision=14)
'{"a_float":{"0":1.0}}'
>>> pd.DataFrame([dict(a_float=0.99999999999999944)]).to_json(double_precision=15)
'{"a_float":{"0":0.1}}'
```
#### Problem description

...

#### Expected Output
```python
'{"a_float":{"0":1.0}}'
```

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

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.12.final.0
python-bits: 64
OS: Linux
OS-release: 4.4.0-66-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: None.None

pandas: 0.19.2
nose: 1.3.7
pip: 9.0.1
setuptools: 34.3.2
Cython: 0.24.1
numpy: 1.12.0
scipy: 0.18.1
statsmodelsdouble_precision: 0.6.1
xarray: None
IPython: 5.1.0
sphinx: 1.4.6
patsy: 0.4.1
dateutil: 2.6.0
pytz: 2016.10
blosc: None
bottleneck: 1.1.0
tables: 3.2.3.1
numexpr: 2.6.1
matplotlib: 1.5.3
openpyxl: 2.3.2
xlrd: 1.0.0
xlwt: 1.1.2
xlsxwriter: 0.9.3
lxml: 3.6.4
bs4: 4.5.1
html5lib: None
httplib2: 0.10.3
apiclient: 1.5.3
sqlalchemy: 1.1.2
pymysql: None
psycopg2: None
jinja2: 2.7.3
boto: 2.42.0
pandas_datareader: None
</details>
