basic sqlite insertion with integer frames does not work
i'm an sql noob, but this seems like it should work without a hitch

```
In [11]: import sqlite3 as sql

In [12]: dfi = DataFrame(randint(10, size=(10, 3)))

In [13]: conn = sql.connect(':memory:')

In [14]: dfi.to_sql('blah', conn)
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-14-25b1bf847714> in <module>()
----> 1 dfi.to_sql('blah', conn)

/home/phillip/Documents/code/py/pandas/pandas/core/frame.pyc in to_sql(self, name, con, flavor, if_exists, **kwargs)
   1519         """
   1520         from pandas.io.sql import write_frame
-> 1521         write_frame(self, name, con, flavor=flavor, if_exists=if_exists, **kwargs)
   1522
   1523     @Appender(fmt.docstring_to_string, indents=1)

/home/phillip/Documents/code/py/pandas/pandas/io/sql.pyc in write_frame(frame, name, con, flavor, if_exists, **kwargs)
    206         create = "DROP TABLE %s" % name
    207     elif not exists:
--> 208         create = get_schema(frame, name, flavor)
    209
    210     if create is not None:

/home/phillip/Documents/code/py/pandas/pandas/io/sql.pyc in get_schema(frame, name, flavor, keys)
    289     lookup_type = lambda dtype: get_sqltype(dtype.type, flavor)
    290     # Replace spaces in DataFrame column names with _.
--> 291     safe_columns = [s.replace(' ', '_').strip() for s in frame.dtypes.index]
    292     column_types = zip(safe_columns, map(lookup_type, frame.dtypes))
    293     if flavor == 'sqlite':

AttributeError: 'numpy.int64' object has no attribute 'replace'
```

i'm guessing this is because `sqlite3` doesn't see `int64` objects as `int`s.
