Use vim-altercmd

ref.
  https://github.com/kana/vim-altercmd/
  http://qiita.com/kentaro/items/c3f7fc1d1be0e106735b
Use bufkill.vim

ref.
  https://github.com/vim-scripts/bufkill.vim
  http://qiita.com/kentaro/items/c3f7fc1d1be0e106735b
Swap BD of bufkill.vim and default bd
Fix AlterCommand configurations

Avoid following warning messages;
  Not an editor command: AlterCommand bd BD
  Not an editor command: AlterCommand BD bd

ref. https://gist.github.com/LeafCage/4085361
Merge branch 'vim-swap-bd'