rollup merge of #20273: alexcrichton/second-pass-comm

rollup merge of #20273: alexcrichton/second-pass-comm

Conflicts:
	src/doc/guide.md
	src/libcollections/bit.rs
	src/libcollections/btree/node.rs
	src/libcollections/slice.rs
	src/libcore/ops.rs
	src/libcore/prelude.rs
	src/librand/rand_impls.rs
	src/librustc/middle/check_match.rs
	src/librustc/middle/infer/region_inference/mod.rs
	src/librustc_driver/lib.rs
	src/librustdoc/test.rs
	src/libstd/bitflags.rs
	src/libstd/io/comm_adapters.rs
	src/libstd/io/mem.rs
	src/libstd/io/mod.rs
	src/libstd/io/net/pipe.rs
	src/libstd/io/net/tcp.rs
	src/libstd/io/net/udp.rs
	src/libstd/io/pipe.rs
	src/libstd/io/process.rs
	src/libstd/io/stdio.rs
	src/libstd/io/timer.rs
	src/libstd/io/util.rs
	src/libstd/macros.rs
	src/libstd/os.rs
	src/libstd/path/posix.rs
	src/libstd/path/windows.rs
	src/libstd/prelude/v1.rs
	src/libstd/rand/mod.rs
	src/libstd/rand/os.rs
	src/libstd/sync/barrier.rs
	src/libstd/sync/condvar.rs
	src/libstd/sync/future.rs
	src/libstd/sync/mpsc/mod.rs
	src/libstd/sync/mpsc/mpsc_queue.rs
	src/libstd/sync/mpsc/select.rs
	src/libstd/sync/mpsc/spsc_queue.rs
	src/libstd/sync/mutex.rs
	src/libstd/sync/once.rs
	src/libstd/sync/rwlock.rs
	src/libstd/sync/semaphore.rs
	src/libstd/sync/task_pool.rs
	src/libstd/sys/common/helper_thread.rs
	src/libstd/sys/unix/process.rs
	src/libstd/sys/unix/timer.rs
	src/libstd/sys/windows/c.rs
	src/libstd/sys/windows/timer.rs
	src/libstd/sys/windows/tty.rs
	src/libstd/thread.rs
	src/libstd/thread_local/mod.rs
	src/libstd/thread_local/scoped.rs
	src/libtest/lib.rs
	src/test/auxiliary/cci_capture_clause.rs
	src/test/bench/shootout-reverse-complement.rs
	src/test/bench/shootout-spectralnorm.rs
	src/test/compile-fail/array-old-syntax-2.rs
	src/test/compile-fail/bind-by-move-no-guards.rs
	src/test/compile-fail/builtin-superkinds-self-type.rs
	src/test/compile-fail/comm-not-freeze-receiver.rs
	src/test/compile-fail/comm-not-freeze.rs
	src/test/compile-fail/issue-12041.rs
	src/test/compile-fail/unsendable-class.rs
	src/test/run-pass/builtin-superkinds-capabilities-transitive.rs
	src/test/run-pass/builtin-superkinds-capabilities-xc.rs
	src/test/run-pass/builtin-superkinds-capabilities.rs
	src/test/run-pass/builtin-superkinds-self-type.rs
	src/test/run-pass/capturing-logging.rs
	src/test/run-pass/closure-bounds-can-capture-chan.rs
	src/test/run-pass/comm.rs
	src/test/run-pass/core-run-destroy.rs
	src/test/run-pass/drop-trait-enum.rs
	src/test/run-pass/hashmap-memory.rs
	src/test/run-pass/issue-13494.rs
	src/test/run-pass/issue-3609.rs
	src/test/run-pass/issue-4446.rs
	src/test/run-pass/issue-4448.rs
	src/test/run-pass/issue-8827.rs
	src/test/run-pass/issue-9396.rs
	src/test/run-pass/ivec-tag.rs
	src/test/run-pass/rust-log-filter.rs
	src/test/run-pass/send-resource.rs
	src/test/run-pass/send-type-inference.rs
	src/test/run-pass/sendable-class.rs
	src/test/run-pass/spawn-types.rs
	src/test/run-pass/task-comm-0.rs
	src/test/run-pass/task-comm-10.rs
	src/test/run-pass/task-comm-11.rs
	src/test/run-pass/task-comm-13.rs
	src/test/run-pass/task-comm-14.rs
	src/test/run-pass/task-comm-15.rs
	src/test/run-pass/task-comm-16.rs
	src/test/run-pass/task-comm-3.rs
	src/test/run-pass/task-comm-4.rs
	src/test/run-pass/task-comm-5.rs
	src/test/run-pass/task-comm-6.rs
	src/test/run-pass/task-comm-7.rs
	src/test/run-pass/task-comm-9.rs
	src/test/run-pass/task-comm-chan-nil.rs
	src/test/run-pass/task-spawn-move-and-copy.rs
	src/test/run-pass/task-stderr.rs
	src/test/run-pass/tcp-accept-stress.rs
	src/test/run-pass/tcp-connect-timeouts.rs
	src/test/run-pass/tempfile.rs
	src/test/run-pass/trait-bounds-in-arc.rs
	src/test/run-pass/trivial-message.rs
	src/test/run-pass/unique-send-2.rs
	src/test/run-pass/unique-send.rs
	src/test/run-pass/unwind-resource.rs