Rename fail! to panic!

https://github.com/rust-lang/rfcs/pull/221

The current terminology of "task failure" often causes problems when
writing or speaking about code. You often want to talk about the
possibility of an operation that returns a Result "failing", but cannot
because of the ambiguity with task failure. Instead, you have to speak
of "the failing case" or "when the operation does not succeed" or other
circumlocutions.

Likewise, we use a "Failure" header in rustdoc to describe when
operations may fail the task, but it would often be helpful to separate
out a section describing the "Err-producing" case.

We have been steadily moving away from task failure and toward Result as
an error-handling mechanism, so we should optimize our terminology
accordingly: Result-producing functions should be easy to describe.

To update your code, rename any call to `fail!` to `panic!` instead.
Assuming you have not created your own macro named `panic!`, this
will work on UNIX based systems:

    grep -lZR 'fail!' . | xargs -0 -l sed -i -e 's/fail!/panic!/g'

You can of course also do this by hand.

[breaking-change]

1 files changed, 5 insertions, 5 deletions

diff --git a/src/libgreen/sched.rs b/src/libgreen/sched.rs
index c465aad3e3b..b1c2695ac7d 100644
--- a/src/libgreen/sched.rs
+++ b/src/libgreen/sched.rs
@@ -761,7 +761,7 @@ impl Scheduler {
         // task-local lock around this block. The resumption of the task in
         // context switching will bounce on the lock, thereby waiting for this
         // block to finish, eliminating the race mentioned above.
-        // fail!("should never return!");
+        // panic!("should never return!");
         //
         // To actually maintain a handle to the lock, we use an unsafe pointer
         // to it, but we're guaranteed that the task won't exit until we've
@@ -806,7 +806,7 @@ impl Scheduler {
             coroutine.recycle(&mut sched.stack_pool);
             sched.task_state.decrement();
         });
-        fail!("should never return!");
+        panic!("should never return!");
     }
 
     pub fn run_task(self: Box<Scheduler>,
@@ -1054,7 +1054,7 @@ mod test {
                 task.put_runtime(green);
                 return ret;
             }
-            None => fail!()
+            None => panic!()
         }
     }
 
@@ -1202,8 +1202,8 @@ mod test {
                     }))) => {
                         *id == sched_id
                     }
-                    TypeGreen(None) => { fail!("task without home"); }
-                    TypeSched => { fail!("expected green task"); }
+                    TypeGreen(None) => { panic!("task without home"); }
+                    TypeSched => { panic!("expected green task"); }
                 };
                 task.put();
                 ret