mapRange-generated Ranges should be laws-tested

[julienrf]

See the discussion here: scala/collection-strawman#200 (comment)

[SethTisue]

@Ichoran interested in finishing this off...?

[SethTisue]

@Ichoran is this an RC1 blocker?

[Ichoran]

I don't know if it's a blocker. It'd be good to get them in.

[Ichoran]

I think we'll have to leave this for RC2. I don't have time now.