Issue with `position: relative` on container in alpha 6

Created by: ilyavolodin

Alpha 6 introduced a minor change to container class with this PR: https://github.com/twbs/bootstrap/commit/d9fcdcfa767c7579e90e334f42457b9b5378f67d Even though it's a one-line change, it has a huge effect on layout, since if you are using Bootstrap grid for page layouts, it's now impossible to create absolutely positioned to screen elements from inside the grid. Having position: relative on container is very limiting. Unfortunately PR that was merged doesn't really explain why this change has been made other then in the title. There's a comment on the PR https://github.com/twbs/bootstrap/pull/21464#issuecomment-269627888 that basically says the same thing as this issue (but it's not clear if it's supporting the change or warning against it).

Is this something that can be reverted in the future releases?