Inexact result on floating-point remainder

This seems to be a regression in 11.0 or in master (note the values are exactly representable):

```
>>> np.remainder(3, 2.5)
0.49999999999999989
>>> np.__version__
'1.12.0.dev0+58263eb'
```

Compare to:

```
>>> np.remainder(3, 2.5)
0.5
>>> np.__version__
'1.10.4'
```
