Implement Zero for unit
Remove unused variables.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Give tasks useful names. #2891
Move atomically to unstable::sync, and document what it actually does. Close #7872.
std: Remove PortSet. Not supported by new scheduler. Replace uses with SharedChan.
test: add more codegen tests, add copyright headers to all.
mk/tests.mk: fix typo "srcrustllvm"
mk/tests.mk: remove mention of nonexistent files
auto merge of #8149 : omasanori/rust/cleanup, r=alexcrichton

Fixed a warning.
rc: from_{owned,const} -> from_{send,freeze}
migrate many `for` loops to `foreach`
auto merge of #8184 : thestinger/rust/retreat, r=huonw
auto merge of #8155 : stepancheg/rust/unit-zero, r=alexcrichton
auto merge of #8158 : bblum/rust/task-cleanup, r=brson

r? @brson
auto merge of #8164 : brson/rust/noportset, r=pcwalton

...haredChan.
std: Use `do` blocks instead of `for` with .iter_bytes()
extra: Use `do` instead of `for` in extra::iter
std: Replace `for` with `do { .. }` expr where internal iterators are used
extra: Replace `for` with `do { .. }` expr where internal iterators are used
extra: Use external iterators in bitv implementation

Convert some internally used functions to use a external iterators.

Change all uses of remaining internal iterators to use `do` expr