* minibuffer.el (completion-common-substring): Mark obsolete.

* minibuffer.el (completion-common-substring): Mark obsolete.
(completions-first-difference, completions-common-part): Move from simple.el.
(completion-hilit-commonality): New fun.
(display-completion-list, completion-emacs21-all-completions)
(completion-emacs22-all-completions): Use it.
* simple.el (completions-first-difference, completions-common-part):
Move to minibuffer.el.
(choose-completion-string): Use field functions and minibufferp.
(completion-setup-function): Don't set completions faces.