modified logging function to truncate output and adjusted error output formatting tests to be compatible with both the new and old runtimes
fixed the buffer to make it a more reasonable size
option: mutate() and mutate_default() should return bool

Fixes #8047.
std: use ptr.offset where possible in the vec iterator.

Closes #8212.
std: add benchmark for vec.mut_iter.
Explicitly impl Clone for RWArc

RWArc had a clone() method, but it was part of impl RWArc instead of
an implementation of Clone.

Stick with the explicit implementation instead of deriving Clone so we
can have a docstring.

Fixes #8052.
Remove unused variables.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Rename sum -> _sum.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Move `use` statements.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
auto merge of #8257 : mozilla/rust/rollup, r=thestinger

1f9c392 r=brson
54e685d r=graydon
1992765 r=thestinger
75155cd r=bblum
def8891 r=graydon