Fix chebpts rescale

This is to address #1202. Now the barycentric weights are rescaled.
```
>> [x, w, v] = chebpts(4, 1)
x =
   -0.9239
   -0.3827
    0.3827
    0.9239
w =
    0.2643    0.7357    0.7357    0.2643
v =
   -0.4142
    1.0000
   -1.0000
    0.4142
```
@nickhale What is the benefit of such a rescaling? If there isn't much we gain, shall we just leave the code as it is but change the help text?