Pycharm linter flags output of concat as "type", not DataFrame

#### Minimum display example 
```python
df1 = pd.DataFrame({'A': ['A0']}, index=[0])
df2 = pd.DataFrame({'A': ['A4']}, index=[4])
result = pd.concat([df1, df2])

print(df1.loc[4])  # Pycharm doesn't flag
print(result.loc[4])  # Pycharm flags as "Unresolved attribute reference '.loc' for class 'type'"
                      # But runs fine anyway
```

#### Problem description
Pycharm's linter believes pd.concat as returning class "type", when it normally returns a dataframe.

I suspect that this is due to core.reshape.concat._Concatenator.get_result() using core.dtypes.concat._get_frame_result_type which sometimes returns SparseDataFrame (a type) and sometimes an object (normally a Dataframe?).

#### Extract from pandas.core.dtypes.concat

```python
def _get_frame_result_type(result, objs):
    """
    return appropriate class of DataFrame-like concat
    if any block is SparseBlock, return SparseDataFrame
    otherwise, return 1st obj
    """
    if any(b.is_sparse for b in result.blocks):
        from pandas.core.sparse.api import SparseDataFrame
        return SparseDataFrame
    else:
        return objs[0]
```

#### Expected Output
The MDE should not throw an error in Pycharm.

#### Output of ``pd.show_versions()``
<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.6.2.final.0
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 94 Stepping 3, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.20.3
pytest: None
pip: 9.0.1
setuptools: 28.8.0
Cython: None
numpy: 1.13.1
scipy: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.6.1
pytz: 2017.2
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: None
openpyxl: 2.4.8
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: 4.6.0
html5lib: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: None
s3fs: None
pandas_gbq: None
pandas_datareader: None
None
</details>
I am using Pycharm Community Edition 2017.1.5.


