Fix documentation for slice()

Fixes https://github.com/mozilla/rust/issues/14577

src/libcollections/vec.rs

@@ -782,11 +782,11 @@ impl<T> Vec<T> {
         self.as_mut_slice().sort_by(compare)
     }
 
-    /// Returns a slice of `self` between `start` and `end`.
+    /// Returns a slice of self spanning the interval [`start`, `end`).
     ///
     /// # Failure
     ///
-    /// Fails when `start` or `end` point outside the bounds of `self`, or when
+    /// Fails when the slice (or part of it) is outside the bounds of self, or when
     /// `start` > `end`.
     ///
     /// # Example

src/libcore/slice.rs

@@ -366,9 +366,9 @@ impl<T> Container for ~[T] {
 /// Extension methods for vectors
 pub trait ImmutableVector<'a, T> {
     /**
-     * Returns a slice of self between `start` and `end`.
+     * Returns a slice of self spanning the interval [`start`, `end`).
      *
-     * Fails when `start` or `end` point outside the bounds of self,
+     * Fails when the slice (or part of it) is outside the bounds of self,
      * or when `start` > `end`.
      */
     fn slice(&self, start: uint, end: uint) -> &'a [T];