emacs-helm/helm — pull request #16 by tarsius (2012-03-18 15:58:11+00:00)
Title: define helm-command-prefix without destroying existing keymap

This renames the command from `helm-command-map` to `helm-command-prefix`. The mapvar is still named `helm-command-map`. The keymap is now defined inside the `defvar` call. Because `define-prefix-command` wips an existing keymap it is wrapped with `let` so that the existing value can be restored.

Before this change another hack was used to deal with the fact that `define-prefix-command` erases an existing keymap (all bindings defined at the top-level). This is a different hack which additionally protects bindings in `helm-command-map` that are defined in other files but `helm-config.el`.