#N/A: Add new git_branch_delete_checked_out rule

[scorphus]

Add a new rule to delete the currently checked out branch, if so desired:

$ git checkout -b foo
Switched to a new branch 'foo'
$ git branch -d foo
error: Cannot delete branch 'foo' checked out at '/Users/scorphus/Workspace/thefuck'
$ fuck
git checkout master; and git branch -D foo [enter/↑/↓/ctrl+c]
Switched to branch 'master'
Your branch is up to date with 'origin/master'.
Deleted branch foo (was 34872f1).

[nvbn]

Looks good, thanks!