Error message thrown by merge is not helpful.

```python
# Your code here
df1 = pd.DataFrame( {'A' : [1,2,3]})
df2 = pd.DataFrame({'B': [1,4,5]})
pd.merge([df1,df2], left_index=True,right_index=True)

TypeError                                 Traceback (most recent call last)
<ipython-input-28-1a158d54d1f6> in <module>()
pd.merge([df1,df2], left_index=True,right_index=True)

TypeError: merge() takes at least 2 arguments (3 given)

```
#### Problem description
The error message thrown is because the merge function expects two non-keyword args. However the current error message is unhelpful and a bit confusing.

#### Expected Output
```
TypeError(): merge() takes at least 2 non-keyword arguments (1 given)
```
#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 2.7.13.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: None.None

pandas: 0.21.0
pytest: None
pip: 9.0.1
setuptools: 32.1.0
Cython: None
numpy: 1.13.3
scipy: 0.19.1
pyarrow: None
xarray: None
IPython: 5.4.1
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: 4.6.0
html5lib: 0.9999999
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.9.6
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None
</details>
