Completion: Slowness Explained

[T.V Raman]

Starting this as a new thread  to summarize  two snowness issues I've been
reporting on separate threads --

1. completion-at-point slows down if completion-auto-help is set to
   always.

   I hadnpt touched that var in a long while, ie slowness emerged last
   week, but the fix is to set that  to its standard value and
   completion-at-point slowness goes away.

   2. minibuffer-visible-completions -- I turned this new option on as
      soon as it became available, later noticed that  in cases like:

      C-h f next- <tab> resulted in some delay before the arrow keys
      started working.

      Turns out I had option  completions-detailed turned on; turning
      that off makes arrow keys snappy when
      minibuffer-visible-completions is on.
      
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