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, 1 insertions, 1 deletions

diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index 3dceb42e206..525d588d70f 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -1349,7 +1349,7 @@ checked_impl!(CheckedMul, checked_mul, i16, intrinsics::i16_mul_with_overflow)
 checked_impl!(CheckedMul, checked_mul, i32, intrinsics::i32_mul_with_overflow)
 checked_impl!(CheckedMul, checked_mul, i64, intrinsics::i64_mul_with_overflow)
 
-/// Performs division that returns `None` instead of failing on division by zero and instead of
+/// Performs division that returns `None` instead of panicking on division by zero and instead of
 /// wrapping around on underflow and overflow.
 pub trait CheckedDiv: Div<Self, Self> {
     /// Divides two numbers, checking for underflow, overflow and division by zero. If any of that