pandas.DataFrame.to_html() munges timestamp objects when formatters are used
{ python 2.6.6, pandas 0.13, numpy 1.6.2 }

A pandas DataFrame containing a Timestamp-type column will display itself nicely in HTML if formatters are unused.  However, if the user employs the `formatters` argument to set column-wise formatting, then the timestamp objects are somehow munged before reaching the given format function.

This is most easily investigated in an iPython notebook:

```
from IPython.display import HTML
df=pandas.DataFrame( {'a':range(3),
                      'b':[
                           pandas.tslib.Timestamp('2013-08-01 09:03:35.013748', tz=None),
                           pandas.tslib.Timestamp('2013-08-01 10:03:35.013748', tz=None),
                           pandas.tslib.Timestamp('2013-08-01 11:03:35.013748', tz=None),
                           ]
                      } )
from numbers import Number
def fmt(x):
    if not isinstance(x, Number):
        return str(x)+': '+x.__class__.__name__
    else:
        return '%.1f'%x

HTML(df.to_html(formatters=[fmt,fmt]))
```

The expected output would show a table whose second column includes string versions of datetimes in 2013.  Instead we see nonsensical times from 1970.
