Fix indentation of throws without result type

Example:

```swift
func f() throws
func g(f: () throws -> Int) rethrows
func h()
```

Fix #172.

Author: taku0

swift-mode-lexer.el

@@ -430,7 +430,7 @@ Return nil otherwise."
        ;; Suppress implicit semicolon around keywords that cannot start or end
        ;; statements.
        (member (swift-mode:token:text previous-token)
-               '("some" "inout" "throws" "rethrows" "in" "where"))
+               '("some" "inout" "in" "where"))
        (member (swift-mode:token:text next-token)
                '("some" "inout" "throws" "rethrows" "in" "where")))
       nil)

test/swift-files/indent/declarations.swift

@@ -573,7 +573,9 @@ struct Foo
 // Protocol declarations
 
 protocol Foo {
-    func foo(x, y) throws -> (A, B)
+    func foo(x: Int, y: Int) throws -> (A, B)
+    func bar(x: Int) throws
+    func baz(x: () throws -> Int) rethrows
     init<A, B>(x: Int) throws
       where
         A: C