enlightenment tweak (trunk only)

enlightenment tweak (trunk only)

     Yesterday's changes made it possible to use ^X to recognize an
unknown ring as one of sustain ability by checking whether wearing the
ring blocks display of base/peak/maximum characteristics when those are
considered to be interesting.  This limits that to cases where the ring
is cursed, so using ^X to figure out the type will leave an undesireable
ring stuck on your finger.  (Both before and after are unnoticeable in
wizard mode, where items which block access to base strength, dex, &c
are overridden by magical disclosure.)