Remove unused imports.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Prefix _ to unused variables.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Append ; to #[allow(dead_code)].

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Add test case for issue #11681
auto merge of #11918 : omasanori/rust/reduce-warnings, r=alexcrichton

Moving forward to green waterfall.
auto merge of #11929 : FlaPer87/rust/issue-11681, r=huonw

closes #11681
Make next_power_of_two generic for unsigned integers

Also rename `next_power_of_two_opt` to `checked_next_power_of_two`.
Remove some unused imports
Remove free-standing div functions in std::uint
Move int and uint overflow tests into macros