Generality creep

[Walter Bright]

On 3/30/2019 12:38 PM, ag0aep6g wrote:
> Then again, Walter has made (limited) efforts to support ranges that are 
> non-assignable due to const fields. Nobody acknowledges that those exact changes 
> also work to accommodate RefRange, but they do.

I'm fine with adjusting `save()` implementations to use construction rather than 
assignment semantics, because that's the way `save()` is defined to behave 
(although it wasn't clearly spelled out).