Missing marker when using `style=...`
There is an issue with the markers in the legend when working with the built-in matplotlib plot-wrapper in pandas. The problem is also in earlier versions and the only workaround I found is using matplotlib directly.

#### A small, complete example of the issue

```python
import pandas as pd
import matplotlib.pyplot as plt

df = pd.DataFrame({'A': [1, 2, 3, 4, 5, 6],
                   'B': [2, 4, 1, 3, 2, 4],
                   'C': [3, 3, 2, 6, 4, 2],
                   'X': [1, 2, 3, 4, 5, 6]})

fig, ax = plt.subplots()

for kind in 'ABC':
    df.plot('X', kind, label=kind, ax=ax, style='.')

plt.show()
```
![markers](https://cloud.githubusercontent.com/assets/1730350/19929894/f55dbd60-a105-11e6-980a-e105b841e518.png)


#### Expected Output
The markers in the legend are missing, except for the last label. It however works if I don't use `style=...`, but the default line-plot, like in this example:
```python
import pandas as pd
import matplotlib.pyplot as plt

df = pd.DataFrame({'A': [1, 2, 3, 4, 5, 6],
                   'B': [2, 4, 1, 3, 2, 4],
                   'C': [3, 3, 2, 6, 4, 2],
                   'X': [1, 2, 3, 4, 5, 6]})

fig, ax = plt.subplots()

for kind in 'ABC':
    df.plot('X', kind, label=kind, ax=ax)

plt.show()
```
![markers_with_lines](https://cloud.githubusercontent.com/assets/1730350/19929965/4d4cea46-a106-11e6-8b30-3d2f361186bb.png)



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

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.5.2.final.0
python-bits: 64
OS: Darwin
OS-release: 16.1.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: en_US.UTF-8
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.19.0
nose: None
pip: 8.1.2
setuptools: 25.2.0
Cython: 0.24.1
numpy: 1.11.2
scipy: 0.18.1
statsmodels: None
xarray: None
IPython: 5.1.0
sphinx: None
patsy: None
dateutil: 2.5.3
pytz: 2016.7
blosc: None
bottleneck: None
tables: 3.3.0
numexpr: 2.6.1
matplotlib: 1.5.3
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.8
boto: None
pandas_datareader: None
</details>