libstd: Change all uses of `&fn(A)->B` over to `|A|->B` in libstd
libextra: Convert uses of `&fn(A)->B` to `|A|->B`.
libsyntax: Change all uses of `&fn` to `||`.
auto merge of #10568 : pcwalton/rust/more-bars, r=alexcrichton

r? @alexcrichton