Add more explicit helpless reasons

Instead of just "while helpless", the death reason will tell
more explicitly why the player was helpless.  For example:
"while frozen by a monster's gaze"

src/decl.c

@@ -21,6 +21,7 @@ char *catmore = 0;		/* default pager */
 NEARDATA int bases[MAXOCLASSES] = DUMMY;
 
 NEARDATA int multi = 0;
+const char *multi_reason = NULL;
 NEARDATA int nroom = 0;
 NEARDATA int nsubroom = 0;
 NEARDATA int occtime = 0;