#[deriving(Clone)] doesn't work for structs with borrowed pointers

[stepancheg]

Code:

#[deriving(Clone)]
struct Foo<'a> {
    s: &'a String,
}

Compiler produces the message:

tmp.rs:3:5: 3:18 error: mismatched types: expected `&collections::string::String`, found `collections::string::String` (expected &-ptr, found struct collections::string::String)
tmp.rs:3     s: &'a String,
             ^~~~~~~~~~~~~
note: in expansion of #[deriving]
tmp.rs:1:1: 1:19 note: expansion site
error: aborting due to previous error

[huonw]

Dupe of #15689. Thanks for filing!