Use milkypostman's `after' macro
Move diminish code to single file
Reorganize init-external.el
Set diff-{command,switches}

My shell 'diff' is an alias for 'colordiff', so I need to point
`diff-command' to 'bin/diff'.
Add diff and ediff to external-map
Advise diff to select buffer and enter view-mode
Add revert-buffer binding to diff-mode-map
Fix docstring typo
Add km/magit-backup-branch