Inline Finallyalizer::drop, allowing LLVM to optimize finally.

* fixes the vec::from_elem regression caused by #8780
* added 5 benchmarks for allocating a 1KB ~[u8] and zeroing it

src/libstd/unstable/finally.rs

@@ -62,6 +62,7 @@ struct Finallyalizer<'a> {
 
 #[unsafe_destructor]
 impl<'a> Drop for Finallyalizer<'a> {
+    #[inline]
     fn drop(&mut self) {
         (self.dtor)();
     }