Revert "Don't anchor :dia completions". The reason we anchor :dia,

is that once you know which :dialog you want to open, you can usually
open it with :dia xy<tab> very quickly and reliable. The difference
to :emenu is that :emenu has lots of completion items with the same
prefix, so anchored completions wouldn't really be that helpful to
quickly open a menu.

This reverts commit fa842fd716aac599891a53efdf64cab76422c153.

common/content/completion.js

@@ -1432,7 +1432,6 @@ function Completion() //{{{
         dialog: function dialog(context)
         {
             context.title = ["Dialog"];
-            context.anchored = false;
             context.completions = config.dialogs;
         },