Fatal Stack Overflow Stemming From Misuse of astype('category')
#### Code Sample

```
import pandas as pd
foo = pd.DataFrame([{'a':'hello'}])
bar = pd.concat([foo,foo], axis=1)
bar.astype('category') # this will make it go boom

```
#### Problem description

As evidenced above, I hit a stack overflow from an error on my end when attempting to cast a column that appears twice in a DataFrame from a careless `pd.concat(, axis=1)`. This error led to a fatal stack overflow error that kills the Python session with the following error...

```
Fatal Python error: Cannot recover from stack overflow.

Current thread 0x00007fff9d7f83c0 (most recent call first):
  File "<frozen importlib._bootstrap>", line 165 in _get_module_lock
  File "<frozen importlib._bootstrap>", line 148 in __enter__
...
  File "/Users/filippiasevoli/anaconda/lib/python3.6/site-packages/pandas/util/_decorators.py", line 178 in wrapper
  File "/Users/filippiasevoli/anaconda/lib/python3.6/site-packages/pandas/core/generic.py", line 4996 in <genexpr>
  File "/Users/filippiasevoli/anaconda/lib/python3.6/site-packages/pandas/core/reshape/concat.py", line 256 in __init__
  ...
Abort trap: 6
```


#### Expected Output

Informative error, not a fatal.


<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.6.1.final.0
python-bits: 64
OS: Darwin
OS-release: 16.7.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.23.4
pytest: 3.0.7
pip: 9.0.1
setuptools: 40.2.0
Cython: 0.25.2
numpy: 1.15.2
scipy: 1.1.0
pyarrow: None
xarray: 0.10.0
IPython: 5.3.0
sphinx: 1.5.6
patsy: 0.5.0
dateutil: 2.7.3
pytz: 2018.5
blosc: None
bottleneck: 1.2.1
tables: 3.3.0
numexpr: 2.6.5
feather: None
matplotlib: 2.0.2
openpyxl: 2.4.7
xlrd: 1.0.0
xlwt: 1.2.0
xlsxwriter: 0.9.6
lxml: 3.7.3
bs4: 4.6.0
html5lib: 0.999
sqlalchemy: 1.2.9
pymysql: None
psycopg2: 2.7.3.1 (dt dec pq3 ext lo64)
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None

</details>
