swift234

[stdlib] Add Interval support

This allows 0.0..<10.3 and 0.1...4.4 to work properly in pattern
matching.

Fixes <rdar://problem/12016900> (#Seed 4: add a "contains" method to the
range types) by making "contains" available on Interval

Addresses <rdar://problem/16254937> (#Seed 4: Ranges with negative
strides are broken) by making the formation of an invalid Interval a
runtime error.

Fixes <rdar://problem/16304317> (Range<T> has limited awesomeness: it is
restricted to types that conform to ForwardIndex)

Fixes <rdar://problem/16736924> (#Seed 4: Enable range inclusion pattern
matching for all types that conform to Equatable and Comparable)

Addresses <rdar://problem/16846325> (#Seed 4: Introduce index range) by
distinguishing Range (which operates on indices) from Interval

Fixes <rdar://problem/17051263> (Pattern-matching a Double range with an
infinite endpoint triggers an assertion failure)

Fixes <rdar://problem/17051271> (#Seed 4: Pattern-matching Double ranges
excludes fractional values)

Addresses <rdar://problem/17171420> (Separate types for closed and
half-open ranges)

Swift SVN r19900