When a buffer-view is set as the view of a Drei instance, invalidate all redisplay information.
When a buffer-view is set as the view of a Drei instance, invalidate
all redisplay information.

This fixes a bug in Climacs where old and erroneous redisplay
information could be kept when a view was hidden, and then brought
back.

informatimago/mcclim,quek/mcclim,quek/mcclim,informatimago/mcclim