crystal helmet

Discussed a long time ago, change helm of brilliance from iron to
crystal so that it doesn't need to be a special case for metallic
armor's affect on spell casting.  It now has a fixed description of
"crystal helmet" but is not pre-discovered.

Add new helm of caution to retain the "etched helmet" description
among the shuffled helms.  Wearing it confers the Warning attribute.
That's fairly lame but not necessarily useless.  It's iron and gets
half the former probability for a random piece of armor being helm
of brilliance so is not likely to be popular.

Helm of caution keeps the old helm of brilliance tile and new helm
of brilliance is basically the same image with different color and
pointed on the top.

Not changed:  the etched helmet was marked as green and is drawn
that way for text but the tile doesn't actually use green for it.
Crystal helmet started as hi_glass (rendered as 'bright cyan') but
has been changed to clr_white to match crystal plate mail.

Old save and bones files are invalidated.

include/objects.h

@@ -441,22 +441,29 @@ HELM("fedora", NoDes,
                                                         FEDORA),
 HELM("cornuthaum", "conical hat",
      0, 1, CLAIRVOYANT,  3, 1,  4, 80, 10, 1, CLOTH, CLR_BLUE,
-                                                        CORNUTHAUM),
         /* name coined by devteam; confers clairvoyance for wizards,
            blocks clairvoyance if worn by role other than wizard */
+                                                        CORNUTHAUM),
 HELM("dunce cap", "conical hat",
      0, 1,           0,  3, 1,  4,  1, 10, 0, CLOTH, CLR_BLUE,
+        /* sets Int and Wis to fixed value of 6, so actually provides
+           protection against death caused by Int being drained below 3 */
                                                         DUNCE_CAP),
 HELM("dented pot", NoDes,
      1, 0,           0,  2, 0, 10,  8,  9, 0, IRON, CLR_BLACK,
                                                         DENTED_POT),
+HELM("helm of brilliance", "crystal helmet",
+     0, 1,           0,  3, 1, 40, 50,  9, 0, GLASS, CLR_WHITE,
+        /* used to be iron and shuffled as "etched helmet" but required
+           special case for the effect of iron armor on spell casting */
+                                                        HELM_OF_BRILLIANCE),
 /* with shuffled appearances... */
 HELM("helmet", "plumed helmet",
      0, 0,           0, 10, 1, 30, 10,  9, 0, IRON, HI_METAL,
                                                         HELMET),
-HELM("helm of brilliance", "etched helmet",
-     0, 1,           0,  6, 1, 50, 50,  9, 0, IRON, CLR_GREEN,
-                                                        HELM_OF_BRILLIANCE),
+HELM("helm of caution", "etched helmet",
+     0, 1,     WARNING,  3, 1, 50, 50,  9, 0, IRON, CLR_GREEN,
+                                                        HELM_OF_CAUTION),
 HELM("helm of opposite alignment", "crested helmet",
      0, 1,           0,  6, 1, 50, 50,  9, 0, IRON, HI_METAL,
                                                  HELM_OF_OPPOSITE_ALIGNMENT),