Issue Description:

Function overload resolution behavior has changed in Swift 3 regarding picking the most narrow available overload for closure types. For example:

func f<T>(_ a: T) {
    print("Wide")
}

func f(_ a: (Int)->(Int)) {
    print("Narrow")
}

f({(a: Int) -> Int in return a + 1})

In Swift 2.x this prints "Narrow", but in Swift 3.0 it prints "Wide." If the argument were of type Int instead of an (Int) -> Int (and the function was called with an appropriate argument) it would print "Narrow" under both Swift 3 and Swift 2.x. Not sure if this change was intentional or not but I didn't see it mentioned in any swift-evolution proposal or otherwise documented.