Pattern reborrows get assigned the wrong lifetime in for loops' LHS.

[eddyb]

These two work:

fn foo<'a>(v: &'a [uint], f: |&'a uint|) {
    for x in v.iter() { f(x); }
}

fn foo<'a>(v: &'a [uint], f: |&'a uint|) {
    for x in v.iter() {
        let  &ref x = x;
        f(x);
    }
}

This doesn't:

fn foo<'a>(v: &'a [uint], f: |&'a uint|) {
    for &ref x in v.iter() { f(x); }
}

error: borrowed value does not live long enough
fn foo<'a>(v: &'a Vec<uint>, f: |&'a uint|) {for &ref x in v.iter() {f(x);}}
                                                           ^~~~~~~~
note: reference must be valid for the lifetime 'a as defined on the block...
fn foo<'a>(v: &'a Vec<uint>, f: |&'a uint|) {for &ref x in v.iter() {f(x);}}
                                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
note: ...but borrowed value is only valid for the block
fn foo<'a>(v: &'a Vec<uint>, f: |&'a uint|) {for &ref x in v.iter() {f(x);}}
                                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The patterns may seem redundant, but while the original code had &(_, ref x), that is not necessary to demonstrate the issue.
The error suggests the lifetime used for x is the lifetime of the v.iter() rvalue, instead of 'a from slice::Items<'a, uint>.

cc @pcwalton