fix #H4919 - vomit message sequencing

The countdown for delayed vomiting gave message "you suddenly vomit!"
at T-2, allowing you to move some more, then vomit at T-0 with no
message, finally at T+2 get "you can move again", making it seem as
if the program was letting you move during a time it thought that you
couldn't move.  Also, there was nothing "sudden" about it since it was
near the end of a 15 or so turn sequence where a few other messages
are given leading up to that.

Change it to
T-2: You are about to vomit.  // different wording
T-0: You vomit!               // new message
so that "you can move again" more clearly refers to the actual event.

src/eat.c

@@ -3129,9 +3129,15 @@ vomit() /* A good idea from David Neves */
         Your("jaw gapes convulsively.");
     else
         make_sick(0L, (char *) 0, TRUE, SICK_VOMITABLE);
-    nomul(-2);
-    multi_reason = "vomiting";
-    nomovemsg = You_can_move_again;
+
+    /* nomul()/You_can_move_again used to be unconditional, which was
+       viable while eating but not for Vomiting countdown where hero might
+       be immobilized for some other reason at the time vomit() is called */
+    if (multi >= -2) {
+        nomul(-2);
+        multi_reason = "vomiting";
+        nomovemsg = You_can_move_again;
+    }
 }
 
 int