Open Radar

 
Summary:
Accessing tuple indexes via labels results in a `does not have a member named` error.

Steps to Reproduce:
1. 
```swift
let (one, two) = [ Void() ].reduce(
	(one: 1, two: 2)
) { previous, value in
	_ = previous.one
	return (previous.one, previous.two)
}
```

Expected Results:
It should compile.

Actual Results:
```
error: libarclite_macosx.a(arclite.o) failed to load objfile for /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/arc/libarclite_macosx.a
Welcome to Apple Swift version 2.0 (700.0.38.1 700.0.53). Type :help for assistance.
repl.swift:4:7: error: '(Int, Int)' does not have a member named 'one'
         _ = previous.one
             ^        ~~~
repl.swift:5:10: error: '(Int, Int)' does not have a member named 'one'
        return (previous.one, previous.two)
                ^        ~~~
```

Regression:
With Swift 1.2 — `swiftlang-602.0.53.1`, the first code block compiles.

Notes:
With Swift 2.0 — `swiftlang-700.0.38.1`, this compiles:
```swift
let (one, two) = [ Void() ].reduce(
	(one: 1, two: 2)
) { previous, value in
	// _ = previous.one // commented this line out
	return (previous.one, previous.two)
}
```

With Swift 2.0 — `swiftlang-700.0.38.1`, this **does not** compile:
```swift
let (one, two) = [ Void() ].reduce(
	(one: 1, two: 2)
) { previous, value in
	_ = previous.0
	return (previous.one, previous.two)
}
```

With Swift 2.0 — `swiftlang-700.0.38.1`, this compiles:
```swift
let (one, two) = [ Void() ].reduce(
	(one: 1, two: 2)
) { previous, value in
	_ = previous.0
	return (previous.0, previous.1)
}
```
With Swift 2.0 — `swiftlang-700.0.38.1`, this compiles:
```swift
let (one, two) = [ Void() ].reduce(
	(one: 1, two: 2)
) { (previous: (one: Int, two: Int), value) in
	_ = previous.one
	return (previous.one, previous.two)
}
```

See in practice: <https://github.com/jdhealy/PrettyColors/commit/7a1682b7663cfa075d8e9a5ad0c1e096e54968b5>