COMPAT: Floating point fractional hours for timedeltas gives unexpected precision issue
Creating a timedelta with fractional hours gives an unexpected large round-off error.

```
>>> to_timedelta(1.0/3, unit='h')
Timedelta('0 days 00:19:59.998800')
```

This is indicates a precision around 2x10^-7  ( 1/(1000_60_60) ), which is less than a single precision float.
