Switch missing_copy_implementations to default-allow

This was particularly helpful in the time just after OIBIT's
implementation to make sure things that were supposed to be Copy
continued to be, but it's now creates a lot of noise for types that
intentionally don't want to be Copy.

src/libcore/hash/sip.rs

@@ -30,7 +30,6 @@ use super::{Hasher, Writer};
 /// strong, this implementation has not been reviewed for such purposes.
 /// As such, all cryptographic uses of this implementation are strongly
 /// discouraged.
-#[allow(missing_copy_implementations)]
 pub struct SipHasher {
     k0: u64,
     k1: u64,

src/libcore/marker.rs

@@ -396,7 +396,6 @@ pub struct InvariantLifetime<'a>;
            reason = "likely to change with new variance strategy")]
 #[lang="no_copy_bound"]
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord)]
-#[allow(missing_copy_implementations)]
 pub struct NoCopy;
 
 /// A type which is considered managed by the GC. This is typically
@@ -405,5 +404,4 @@ pub struct NoCopy;
            reason = "likely to change with new variance strategy")]
 #[lang="managed_bound"]
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord)]
-#[allow(missing_copy_implementations)]
 pub struct Managed;

src/libcore/str/mod.rs

@@ -149,7 +149,6 @@ impl FromStr for bool {
 
 /// An error returned when parsing a `bool` from a string fails.
 #[derive(Debug, Clone, PartialEq)]
-#[allow(missing_copy_implementations)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct ParseBoolError { _priv: () }