Pandas IO to_sql extremely slow when checking for potentially case sensitivity issues
This is related to #7815

Since this fix, when checking for case sensitivity issues for MySQL using InnoDB engine with large numbers of tables, Class SQLDatabase.to_sql can take a long time (I currently have ~30,000 tables and this call takes ~10 seconds).
This is due to the 'SHOW FULL TABLES' call coming from SQLAlchemy, from these lines of code specifically

``` python
engine = self.connectable.engine
with self.connectable.connect() as conn:
    table_names = engine.table_names(
        schema=schema or self.meta.schema,
        connection=conn,
     )
```

A suggested fix would be to add a parameter to the `to_sql` function.
The parameter might look something like, `case_check='warn'`
and the fix might be something like

``` python
if case_check == 'raise' and not name.islower():
    raise Exception("table name must be lower case when case_check = 'raise'")
current_code()
if case_check == 'warn':
    engine = self.connectable.engine
    with self.connectable.connect() as conn:
        table_names = engine.table_names(
            schema=schema or self.meta.schema,
            connection=conn,
         )
```

Versions:
## INSTALLED VERSIONS

commit: None
python: 2.7.6.final.0
python-bits: 64
OS: Linux
OS-release: 3.13.0-83-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_IE.UTF-8

pandas: 0.18.0
nose: 1.3.7
pip: 8.1.1
setuptools: 18.2
Cython: 0.23.4
numpy: 1.10.1
scipy: 0.16.1
statsmodels: None
xarray: None
IPython: None
sphinx: 1.3.1
patsy: None
dateutil: 2.4.2
pytz: 2015.7
blosc: None
bottleneck: None
tables: 3.2.0
numexpr: 2.4.6
matplotlib: 1.5.0
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.0.9
pymysql: None
psycopg2: None
jinja2: 2.8
boto: 2.38.0
