Forgot to make accept() home for IO
Make I/O tests use run_in_mt_newsched_task to get more multi-threaded test coverage
Update for_expr docs.
Add with_mem_writer to std::rt::io::mem.

This is in many ways a replacement for the current
std::io::with_str_writer.
auto merge of #8999 : anasazi/rust/multi-threaded-io-tests, r=brson

Resolves #8685
auto merge of #9038 : singingboyo/rust/with-mem-writer, r=anasazi

This is in many ways a replacement for the current std::io::with_str_writer.
Merge remote-tracking branch 'upstream/master'