std: Add init and uninit to mem. Replace direct intrinsic usage

src/libstd/unstable/intrinsics.rs

@@ -288,8 +288,7 @@ extern "rust-intrinsic" {
     /// Create a value initialized to zero.
     ///
     /// `init` is unsafe because it returns a zeroed-out datum,
-    /// which is unsafe unless T is POD. We don't have a POD
-    /// kind yet. (See #4074).
+    /// which is unsafe unless T is Pod.
     pub fn init<T>() -> T;
 
     /// Create an uninitialized value.

src/libstd/unstable/mutex.rs

@@ -92,7 +92,7 @@ mod imp {
     use libc;
     use self::os::{PTHREAD_MUTEX_INITIALIZER, PTHREAD_COND_INITIALIZER,
                    pthread_mutex_t, pthread_cond_t};
-    use unstable::intrinsics;
+    use mem;
 
     type pthread_mutexattr_t = libc::c_void;
     type pthread_condattr_t = libc::c_void;
@@ -208,8 +208,8 @@ mod imp {
     impl Mutex {
         pub unsafe fn new() -> Mutex {
             let mut m = Mutex {
-                lock: intrinsics::init(),
-                cond: intrinsics::init(),
+                lock: mem::init(),
+                cond: mem::init(),
             };
 
             pthread_mutex_init(&mut m.lock, 0 as *libc::c_void);