Prepared std::sys for removal, and made begin_unwind simpler

- `begin_unwind` is now generic over any `T: Any + Send`.
- Every value you fail with gets boxed as an `~Any`.
- Because of implementation details, `&'static str` and `~str` are still
  handled specially behind the scenes.
- Changed the big macro source string in libsyntax to a raw string
  literal, and enabled doc comments there.

src/libstd/unstable/lang.rs

@@ -19,7 +19,7 @@ use rt::borrowck;
 #[cold]
 #[lang="fail_"]
 pub fn fail_(expr: *c_char, file: *c_char, line: size_t) -> ! {
-    task::begin_unwind(expr, file, line);
+    task::begin_unwind_raw(expr, file, line);
 }
 
 #[cold]

src/libstd/unstable/raw.rs

@@ -62,3 +62,33 @@ impl Repr<*Box<String>> for @str {}
 
 // sure would be nice to have this
 // impl<T> Repr<*Vec<T>> for ~[T] {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use cast;
+
+    #[test]
+    fn synthesize_closure() {
+        unsafe {
+            let x = 10;
+            let f: &fn(int) -> int = |y| x + y;
+
+            assert_eq!(f(20), 30);
+
+            let original_closure: Closure = cast::transmute(f);
+
+            let actual_function_pointer = original_closure.code;
+            let environment = original_closure.env;
+
+            let new_closure = Closure {
+                code: actual_function_pointer,
+                env: environment
+            };
+
+            let new_f: &fn(int) -> int = cast::transmute(new_closure);
+            assert_eq!(new_f(20), 30);
+        }
+    }
+}