io.sql issues with Oracle DB 
With Oracle Database Express Edition 11g Release 2 in use as a SQL DB I have tried to reproduce **Writing DataFrames** example from http://pandas.pydata.org/pandas-docs/stable/io.html#io-sql

``` python
import pandas as pd
from cStringIO import StringIO
from sqlalchemy import create_engine

csv_sample = '''id,Date,Col_1,Col_2,Col_3
26,2012-10-18,X,25.7,True
42,2012-10-19,Y,-12.4,False
63,2012-10-20,Z,5.73,True'''

b = StringIO(csv_sample)
data = pd.read_csv(b, index_col=0)

engine_oracle = create_engine('oracle://admin:whatever@localhost:1521/xe')
data.to_sql('data', engine_oracle)
```

The code produces a warning:

> pandas/io/sql.py:1140: UserWarning: The provided table name 'data' is not found exactly as such in the database after writing the table, possibly due to case sensitivity issues. Consider using lower case table names.
>   "using lower case table names.".format(name), UserWarning) 

Nonetheless, the table is written into a DB, except the table has been already created, in which case the write is refused.

Trying in addition to execute:

``` python
df = pd.read_sql_table('data', engine_oracle)
```

brings an error:

> pandas/io/sql.pyc in read_sql_table(table_name, con, schema, index_col, coerce_float, parse_dates, columns, chunksize)
>     333         meta.reflect(only=[table_name])
>     334     except sqlalchemy.exc.InvalidRequestError:
> --> 335         raise ValueError("Table %s not found" % table_name)
>     336 
>     337     pandas_sql = SQLDatabase(con, meta=meta)
> 
> ValueError: Table data not found

On the other hand:

``` python
print pd.io.sql.has_table('data', engine_oracle)
df = pd.read_sql_query('select * from data', engine_oracle)
```

prints **True** and imports DataFrame regularly. It seems like sqlalchemy is a culprit, but

``` python
from sqlalchemy import MetaData, Table
from sqlalchemy.sql import select

metadata = MetaData()
sa_data = Table('data', metadata, autoload=True, autoload_with=engine_oracle)
s = select([sa_data])
conn = engine_oracle.connect()
s = select([sa_data])
result = conn.execute(s)
for row in result:
    print row
```

passes with no issues producing the following output:

> (26, '2012-10-18', 'X', 25.7, 1)
> (42, '2012-10-19', 'Y', -12.4, 0)
> (63, '2012-10-20', 'Z', 5.73, 1)

Also, I have tried the code with sqlite and postgresql and it shows no issues.

Additional info about the pandas and it's dependencies:

> ## INSTALLED VERSIONS
> 
> commit: None
> python: 2.7.8.final.0
> python-bits: 64
> OS: Linux
> OS-release: 3.13.0-39-generic
> machine: x86_64
> processor: x86_64
> byteorder: little
> LC_ALL: None
> LANG: en_US.UTF-8
> 
> pandas: 0.15.1
> nose: 1.3.3
> Cython: 0.20.1
> numpy: 1.9.1
> scipy: 0.14.0
> statsmodels: 0.5.0
> IPython: 2.3.0
> sphinx: 1.2.3
> patsy: 0.2.1
> dateutil: 1.5
> pytz: 2014.9
> bottleneck: None
> tables: 3.1.1
> numexpr: 2.3.1
> matplotlib: 1.3.1
> openpyxl: 1.8.5
> xlrd: 0.9.3
> xlwt: 0.7.5
> xlsxwriter: 0.5.5
> lxml: 3.3.5
> bs4: 4.3.1
> html5lib: 0.999
> httplib2: None
> apiclient: None
> rpy2: None
> sqlalchemy: 0.9.8
> pymysql: None
> psycopg2: 2.4.6 (dt dec pq3 ext)

cx_oracle   5.1.2 is installed through _conda_
