flatten and flatten! methods for ActiveSupport::Duration
No need to require rbconfig as we are using Gem.ruby
Merge pull request #12503 from arunagw/removed-unused-require

No need to require rbconfig as we are using Gem.ruby
Merge pull request #12480 from iwiznia/master

flatten and flatten! methods for ActiveSupport::Duration
no reason to do this column addition and subtraction business