bug#17809: 24.4.50; Completions display

[Juri Linkov]

> - display-buffer-below-selected for completion-at-point
>   that could work like displaying *Marking Files* in Dired
>   to display *Completions* near the point of completion
>   in the current buffer.

I noticed that at-bottom is used instead of better below-selected
for some completion-at-point commands.  For example,
completing a color in the Customization UI displays the
*Completions* at the bottom even when there is no active minibuffer.

Since completion-at-point commands set the value of `this-command'
I wonder wouldn't it be right to check its value?

=== modified file 'lisp/minibuffer.el'
--- lisp/minibuffer.el  2014-07-08 19:15:28 +0000
+++ lisp/minibuffer.el  2014-10-05 21:59:09 +0000
@@ -1811,7 +1811,7 @@ (defun minibuffer-completion-help (&opti
              ;; Use `display-buffer-below-selected' for inline completions,
              ;; but not in the minibuffer (e.g. in `eval-expression')
              ;; for which `display-buffer-at-bottom' is used.
-             ,(if (and completion-in-region-mode-predicate
+             ,(if (and (eq this-command 'completion-at-point)
                        (not (minibuffer-selected-window)))
                   'display-buffer-below-selected
                 'display-buffer-at-bottom))