Refactored int/uint range code in preparation for change to range_rev semantics.

Also added unit tests of range code to test refactoring.  The
num-range-rev.rs test will need to be updated when the range_rev
semantics change.
Switch over to new range_rev semantics; fix #5270.
Fix #5270: another test I did not update properly.
auto merge of #7684 : pnkfelix/rust/fsk-invert-range-rev-halfclosedness-issue5270-2ndpr, r=cmr

Changes int/uint range_rev to iterate over range `(hi,lo]` instead of `[hi,lo)`.

Fix #5270.

Also:
* Adds unit tests for int/uint range functions
* Updates the uses of `range_rev` to account for the new semantics.  (Note that pretty much all of the updates there were strict improvements to the code in question; yay!)
* Exposes new function, `range_step_inclusive`, which does the range `[hi,lo]`, (at least when `hi-lo` is a multiple of the `step` parameter).
* Special-cases when `|step| == 1` removing unnecessary bounds-check.  (I did not check whether LLVM was already performing this optimization; I figure it would be a net win to not leave that analysis to the compiler.  If reviewer objects, I can easily remove that from the refactored code.)

(This pull request is a rebased version of PR #7524, which went stale due to recent unrelated changes to num libraries.)