fails:Enumerator::Lazy#grep sets #size to nil
fails:Enumerator::Lazy#grep on a nested Lazy sets #size to nil
fails:Enumerator::Lazy#grep sets $~ in the block
fails:Enumerator::Lazy#grep sets $~ in the next block with each
fails:Enumerator::Lazy#grep sets $~ in the next block with map
