Mark Range and Range.Inclusive as inlineable classes.

This removes *all* the overhead if all 3 parameters of the
range are constants. For example,

  for (i <- 0 until 10 by 2) { ... }

If the step is either 1 or -1, and either start or end is
constant (very common case), then almost all the overhead is
removed, except for 3 Long operations. For example:

  for (i <- 0 until n) { ... }