auto merge of #6635 : brson/rust/snapshot, r=brson

diff --cc src/libcore/io.rs
Simple merge

diff --cc src/libcore/unstable/lang.rs
Simple merge

diff --cc src/librustc/middle/borrowck/mod.rs
Simple merge

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

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