Change Display:set-noclose to Display:set:no-close and store in attribute.

Change Display:set-noclose to Display:set:no-close and store in attribute.

Using an attribute to store the no-close string simplifies code, and
using "Display:set:" is similar to "doc:set:" and will soon be used to
set any attribute at the display level.

Signed-off-by: NeilBrown <neil@brown.name>