auto merge of #7725 : msullivan/rust/default-methods, r=pcwalton

r?

diff --cc src/librustc/metadata/encoder.rs
Simple merge

diff --cc src/librustc/middle/lint.rs
Simple merge

diff --cc src/librustc/middle/trans/base.rs
Simple merge

diff --cc src/librustc/middle/trans/expr.rs
Simple merge

diff --cc src/librustc/util/ppaux.rs
Simple merge

diff --cc src/libsyntax/ast_util.rs
Simple merge