Tags: patch

Whenever Completion Preview mode shows a completion preview, it also
activates keybindings for commands that interact with that preview, most
notably TAB is bound to completion-preview-insert, which inserts the
suggested completion.  This is implemented via a minor mode
completion-preview-active-mode whose keymap provides these bindings, and
which is enabled when the preview is displayed. 

This all works well, except for when another minor mode, foo-mode, is
enabled, whose keybindings conflict with these active preview bindings.
If foo-mode is defined after completion-preview-active-mode, i.e. if
foo.el is loaded after completion-preview.el, then foo-mode comes first
in minor-mode-map-alist and takes precedence over the bindings in
completion-preview-active-mode-map.

This happens, for example, with eshell-cmpl-mode, a minor mode that is
enabled by default in Eshell, which binds TAB to completion-at-point.
So currently Completion Preview mode doesn't work as expected in Eshell:
when you try to accept the suggested completion (with TAB), you get
completion-at-point instead of completion-preview-insert.

To fix this issue, we need to give the active completion preview
bindings higher precedence than keymaps of minor modes that where
defined after loading completion-preview.el.  The patch below does that
by using minor-mode-overriding-map-alist.  Any thoughts?