auto merge of #14610 : alexcrichton/rust/issue-14008, r=brson

This commit removes the <M: Any + Send> type parameter from Option::expect in
favor of just taking a hard-coded `&str` argument. This allows this function to
move into libcore.

Previous code using strings with `expect` will continue to work, but code using
this implicitly to transmit task failure will need to unwrap manually with a
`match` statement.

[breaking-change]
Closes #14008

src/libstd/slice.rs

@@ -296,7 +296,6 @@ impl<'a, T: Clone> CloneableVector<T> for &'a [T] {
     fn to_owned(&self) -> ~[T] {
         use RawVec = core::raw::Vec;
         use num::{CheckedAdd, CheckedMul};
-        use option::Expect;
 
         let len = self.len();
         let data_size = len.checked_mul(&mem::size_of::<T>());