Allow fail messages to be caught, and introduce the Any trait

Some code cleanup, sorting of import blocks

Removed std::unstable::UnsafeArc's use of Either

Added run-fail tests for the new FailWithCause impls

Changed future_result and try to return Result<(), ~Any>.

- Internally, there is an enum of possible fail messages passend around.
- In case of linked failure or a string message, the ~Any gets
  lazyly allocated in future_results recv method.
- For that, future result now returns a wrapper around a Port.
- Moved and renamed task::TaskResult into rt::task::UnwindResult
  and made it an internal enum.
- Introduced a replacement typedef `type TaskResult = Result<(), ~Any>`.

src/libextra/sync.rs

@@ -918,7 +918,7 @@ mod tests {
         let m = Mutex::new();
         let m2 = m.clone();
 
-        let result: result::Result<(),()> = do task::try {
+        let result: result::Result<(), ~Any> = do task::try {
             do m2.lock {
                 fail!();
             }
@@ -935,7 +935,7 @@ mod tests {
         let m = Mutex::new();
         let m2 = m.clone();
 
-        let result: result::Result<(),()> = do task::try {
+        let result: result::Result<(), ~Any> = do task::try {
             let (p, c) = comm::stream();
             do task::spawn || { // linked
                 let _ = p.recv(); // wait for sibling to get in the mutex
@@ -963,7 +963,7 @@ mod tests {
         let m2 = m.clone();
         let (p, c) = comm::stream();
 
-        let result: result::Result<(),()> = do task::try {
+        let result: result::Result<(), ~Any> = do task::try {
             let mut sibling_convos = ~[];
             do 2.times {
                 let (p, c) = comm::stream();
@@ -1272,7 +1272,7 @@ mod tests {
         let x = RWLock::new();
         let x2 = x.clone();
 
-        let result: result::Result<(),()> = do task::try || {
+        let result: result::Result<(), ~Any> = do task::try || {
             do lock_rwlock_in_mode(&x2, mode1) {
                 fail!();
             }

src/libextra/test.rs

@@ -873,8 +873,7 @@ pub fn run_test(force_ignore: bool,
             task.spawn(testfn_cell.take());
 
             let task_result = result_future.recv();
-            let test_result = calc_result(&desc,
-                                          task_result == task::Success);
+            let test_result = calc_result(&desc, task_result.is_ok());
             monitor_ch.send((desc.clone(), test_result));
         }
     }

src/librustpkg/tests.rs

@@ -640,9 +640,8 @@ fn test_install_invalid() {
                                   pkgid.clone());
         ctxt.install(pkg_src, &WhatToBuild::new(MaybeCustom, Everything));
     };
-    // Not the best test -- doesn't test that we failed in the right way.
-    // Best we can do for now.
-    assert!(result == Err(()));
+    assert!(result.unwrap_err()
+            .to_str().contains("supplied path for package dir does not exist"));
 }
 
 #[test]