[Feature #18982]

Instead of introducing an `exception: false` argument to have `non_block`
return nil rather than raise, we can clearly document that a timeout of 0
immediately returns.

The code is refactored a bit to avoid doing a time calculation in
such case.

[Feature #18774]

As well as `SizedQueue#pop(timeout: sec)`

If both `non_block=true` and `timeout:` are supplied, ArgumentError
is raised.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66041 b2dd03c8-39d4-4d8f-98ff-823fe69b080e