Join or concat int and float by axis=1 would cast int columns to float
#### Code Sample, a copy-pastable example if possible

## Wait ..  below example can't work , I don't know why my dataset would occur this error.

```python

testb = pd.DataFrame({"a": np.ones(5)}).astype(int)
testa = pd.DataFrame({"b": np.zeros(5)}).astype(int)
testc = pd.DataFrame({"c": np.random.rand(5)})
result = pd.concat((testa, testb, testc), axis=1)
print(result)
```
#### Problem description

holiday column was int
![image](https://user-images.githubusercontent.com/3938751/49626056-121ccc80-fa13-11e8-9596-ce6b97430b19.png)

weather2  was int :

![image](https://user-images.githubusercontent.com/3938751/49626465-f4e8fd80-fa14-11e8-8d65-43f7d17e9ac4.png)

discount was float: 
![image](https://user-images.githubusercontent.com/3938751/49626481-07fbcd80-fa15-11e8-8a13-ac813d455bc7.png)


but after `pd.concat`,  it became float
![image](https://user-images.githubusercontent.com/3938751/49626067-219c1580-fa13-11e8-90ad-da05c84bd748.png)


And  join  behaved different:

![image](https://user-images.githubusercontent.com/3938751/49626371-886dfe80-fa14-11e8-9c01-d55aa10e728c.png)


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

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.6.5.final.0
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 45 Stepping 7, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.23.4
pytest: 3.5.1
pip: 18.1
setuptools: 39.1.0
Cython: 0.28.2
numpy: 1.14.3
scipy: 1.1.0
pyarrow: 0.8.0
xarray: None
IPython: 6.4.0
sphinx: 1.7.4
patsy: 0.5.0
dateutil: 2.7.3
pytz: 2018.4
blosc: None
bottleneck: 1.2.1
tables: 3.4.3
numexpr: 2.6.5
feather: None
matplotlib: 3.0.1
openpyxl: 2.5.3
xlrd: 1.1.0
xlwt: 1.3.0
xlsxwriter: 1.0.4
lxml: 4.2.1
bs4: 4.6.0
html5lib: 1.0.1
sqlalchemy: 1.2.7
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: 0.1.6
fastparquet: None
pandas_gbq: None
pandas_datareader: None

</details>
