core: add Reader, Writer, ReaderUtil, WriterUtil to prelude. Close #4182.
add stage3 markers where necessary for dist-snap
libsyntax: Never use `::<>` in the type grammar
librustc: Fix bug preventing `-framework Foo` from working cross-crate.
etc: Suppress Linux valgrind issues for new scheduler
auto merge of #5455 : pcwalton/rust/framework, r=catamorphism

r? @catamorphism
auto merge of #5456 : graydon/rust/fixups, r=pcwalton

Stage markers for stage3 and a trivial prelude fix.
auto merge of #5458 : pcwalton/rust/valgrind-suppress, r=pcwalton