auto merge of #17894 : steveklabnik/rust/fail_to_panic, r=aturon

This in-progress PR implements https://github.com/rust-lang/rust/issues/17489.

I made the code changes in this commit, next is to go through alllllllll the documentation and fix various things.

- Rename column headings as appropriate, `# Panics` for panic conditions and `# Errors` for `Result`s.
- clean up usage of words like 'fail' in error messages

Anything else to add to the list, @aturon ? I think I should leave the actual functions with names like `slice_or_fail` alone, since you'll get to those in your conventions work?

I'm submitting just the code bits now so that we can see it separately, and I also don't want to have to keep re-building rust over and over again if I don't have to :wink: 

Listing all the bits so I can remember as I go:

- [x] compiler-rt
- [x] compiletest
- [x] doc
- [x] driver
- [x] etc
- [x] grammar
- [x] jemalloc
- [x] liballoc
- [x] libarena
- [x] libbacktrace
- [x] libcollections
- [x] libcore
- [x] libcoretest
- [x] libdebug
- [x] libflate
- [x] libfmt_macros
- [x] libfourcc
- [x] libgetopts
- [x] libglob
- [x] libgraphviz
- [x] libgreen
- [x] libhexfloat
- [x] liblibc
- [x] liblog
- [x] libnative
- [x] libnum
- [x] librand
- [x] librbml
- [x] libregex
- [x] libregex_macros
- [x] librlibc
- [x] librustc
- [x] librustc_back
- [x] librustc_llvm
- [x] librustdoc
- [x] librustrt
- [x] libsemver
- [x] libserialize
- [x] libstd
- [x] libsync
- [x] libsyntax
- [x] libterm
- [x] libtest
- [x] libtime
- [x] libunicode
- [x] liburl
- [x] libuuid
- [x] llvm
- [x] rt
- [x] test

2 files changed, 5 insertions, 5 deletions

diff --git a/src/liballoc/arc.rs b/src/liballoc/arc.rs
index cc6f2d76eaf..f543826fe01 100644
--- a/src/liballoc/arc.rs
+++ b/src/liballoc/arc.rs
@@ -227,9 +227,9 @@ impl<T: Sync + Send> Drop for Arc<T> {
 impl<T: Sync + Send> Weak<T> {
     /// Attempts to upgrade this weak reference to a strong reference.
     ///
-    /// This method will fail to upgrade this reference if the strong reference
-    /// count has already reached 0, but if there are still other active strong
-    /// references this function will return a new strong reference to the data.
+    /// This method will not upgrade this reference if the strong reference count has already
+    /// reached 0, but if there are still other active strong references this function will return
+    /// a new strong reference to the data.
     pub fn upgrade(&self) -> Option<Arc<T>> {
         // We use a CAS loop to increment the strong count instead of a
         // fetch_add because once the count hits 0 is must never be above 0.
diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index 168d0daeb38..09404af7027 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -148,11 +148,11 @@ mod test {
 
         match a.downcast::<uint>() {
             Ok(a) => { assert!(a == box 8u); }
-            Err(..) => fail!()
+            Err(..) => panic!()
         }
         match b.downcast::<Test>() {
             Ok(a) => { assert!(a == box Test); }
-            Err(..) => fail!()
+            Err(..) => panic!()
         }
 
         let a = box 8u as Box<Any>;