BUG: DataFrame.align behavior when columns are many-to-many
#### Code Sample

```python
import numpy as np
import pandas as pd

df1 = pd.DataFrame(np.random.random(size=(10, 2)), columns=["a", "a"])
df2 = pd.DataFrame(np.random.random(size=(10, 2)), columns=["a", "a"])

# the first column of df1 is aligned with each column of df2
df1.iloc[:, [0]].align(df2)
# each column of df1 is aligned with only one column of df2
df1.align(df2)
```
#### Problem description

The documentation for `DataFrame.align` says that method performs a join between `self` and `other`, but in the case where the columns are many-to-many this doesn't always seem to be the case.  (In the above example when column `a` is one-to-many it's aligned with each column of `other`, but when the columns are many-to-many the alignment is one-to-one.)  Is this the intended behavior or a bug?

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

<details>

[paste the output of ``pd.show_versions()`` here below this line]

INSTALLED VERSIONS
------------------
commit: None
python: 3.7.2.final.0
python-bits: 64
OS: Darwin
OS-release: 18.2.0
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: 4.0.2
pip: 18.1
setuptools: 40.6.3
Cython: 0.29.2
numpy: 1.15.1
scipy: 1.1.0
pyarrow: 0.11.1
xarray: None
IPython: 7.2.0
sphinx: 1.8.2
patsy: 0.5.0
dateutil: 2.7.5
pytz: 2018.7
blosc: None
bottleneck: 1.2.1
tables: None
numexpr: 2.6.8
feather: None
matplotlib: 2.2.3
openpyxl: 2.5.12
xlrd: 1.2.0
xlwt: 1.3.0
xlsxwriter: 1.1.2
lxml: 4.2.5
bs4: 4.6.3
html5lib: 1.0.1
sqlalchemy: 1.2.15
pymysql: None
psycopg2: 2.7.5 (dt dec pq3 ext lo64)
jinja2: 2.10
s3fs: 0.2.0
fastparquet: None
pandas_gbq: None
pandas_datareader: None

</details>
