Return SizedIteratorRanges from ranges::range for RandomAccessIteratorRanges and SizedIterables

The interface of `ranges::range` consists of:

- `ranges::range(Iterator, Sentinel, Size) -> sized_iterator_range`
- `ranges::range(Iterator, Sentinel) -> iterator_range`

However, when calling `ranges::range(Iterator, Sentinel)` with `RandomAccessIterator`s, we can 
compute the range size in `O(1)` and return a `sized_iterator_range`.

Furthermore, some containers like `std::list` provide only `BidirectionalIterator`s, but they have
an `O(1)` `size()` member function.

This patch changes `ranges::range` interface to: 

- `ranges::range(Iterator, Sentinel, Size) -> sized_iterator_range`
- `ranges::range(Iterator, Sentinel) -> sized_iterator_range` (if possible) / `iterator_range`
- `ranges::range(Iterable&) -> sized_iterator_range` (if possible) / `iterator_range`

The `ranges::range(Iterable&)` dispatches to a `sized_iterator_range` if the `Iterable` has `RandomAccessIterator`s or `ranges::size(Iterable&)` can compute its size (which is `O(1)`). Otherwise it returns an `iterator_range`.

Note:  the `algorithm/equal.cpp` test used to perform one comparison in the modified `CHECK` clause when comparing two `RandomAccessRange`s even tho they had different sizes. Now it doesn't need to perform any comparison at all. 
I know you feel that `std:: pair ` of iterators should model Range, but I'm undecided about that. If we make `pair ` model Range, `size ` will just work for it. What is the `list:: size ` issue you refer to?