fix GitHub issue 1303 related to engravings

GitHub issue reported by ars3niy:
https://github.com/NetHack/NetHack/issues/1303

@ars3niy commented on Oct 27:
Stepping on a square with a dust or "graffiti" engraving while blind
produces no message because presumably you can't read them by swiping
the floor with your hands, however the engraving glyph still shows up on
the map afterwards. While this helps zen players, it looks like a bug.

@ville-v commented 3 days ago:
Searching while blind also reveals the engravings. Here is a save file
demonstrating the issue.
[...]

This adds an erevealed bit to engravings, to accompany the the eread
bit that is already there.

eread:      refers to the text of the engraving
erevealed:  refers to the engraving map symbol

Hopefully, this resolves issue 1303 without creating additional bugs.

This invalidates existing save files and bones.

Fixes #1303

src/engrave.c

@@ -285,6 +285,31 @@ wipe_engr_at(coordxy x, coordxy y, xint16 cnt, boolean magical)
     }
 }
 
+/*
+ * Returns:
+ *    non-zero if it can be felt
+ */
+boolean
+engr_can_be_felt(struct engr *ep)
+{
+    boolean canfeel = FALSE;
+
+    switch (ep->engr_type) {
+        case ENGRAVE:
+        case HEADSTONE:
+        case BURN:
+            canfeel = TRUE;
+            break;
+        case DUST:
+        case MARK:
+        case ENGR_BLOOD:
+        default:
+            canfeel = FALSE;
+            break;
+    }
+    return canfeel;
+}
+
 void
 read_engr_at(coordxy x, coordxy y)
 {
@@ -355,6 +380,7 @@ read_engr_at(coordxy x, coordxy y)
             You("%s: \"%s\".", (Blind) ? "feel the words" : "read", et);
             Strcpy(ep->engr_txt[remembered_text], ep->engr_txt[actual_text]);
             ep->eread = 1;
+            ep->erevealed = 1;
             if (svc.context.run > 0)
                 nomul(0);
         }
@@ -399,7 +425,8 @@ make_engr_at(
     ep->engr_type = (xint8) ((e_type > 0) ? e_type : rnd(N_ENGRAVE - 1));
     ep->engr_szeach = smem;
     ep->engr_alloc = smem * 3;
-    /* we do not set ep->eread; the caller will need to if required */
+    /* we do not set ep->eread or ep->erevealed;
+     * the caller will need to if required */
 }
 
 /* delete any engraving at location <x,y> */
@@ -996,6 +1023,7 @@ doengrave(void)
     if (de->teleengr) {
         rloc_engr(de->oep);
         de->oep->eread = 0;
+        de->oep->erevealed = 0;
         de->disprefresh = TRUE;
         de->oep = (struct engr *) 0;
     }
@@ -1014,6 +1042,7 @@ doengrave(void)
             if (tmp_ep != 0) {
                 pline_The("engraving now reads: \"%s\".", de->buf);
                 tmp_ep->eread = 1;
+                tmp_ep->erevealed = 1;
                 de->disprefresh = TRUE;
             }
         }
@@ -1395,8 +1424,10 @@ engrave(void)
     make_engr_at(u.ux, u.uy, buf, svm.moves - gm.multi,
                  svc.context.engraving.type);
     oep = engr_at(u.ux, u.uy);
-    if (oep)
+    if (oep) {
         oep->eread = 1;
+        oep->erevealed = 1;
+    }
 
     if (*endc) {
         svc.context.engraving.nextc = endc;
@@ -1640,6 +1671,7 @@ void
 feel_engraving(struct engr *ep)
 {
     ep->eread = 1;
+    ep->erevealed = 1;
     map_engraving(ep, 1);
     /* in case it's beneath something, redisplay the something */
     newsym(ep->engr_x, ep->engr_y);