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"

include/decl.h

@@ -28,6 +28,7 @@ E char SAVEP[];
 E NEARDATA int bases[MAXOCLASSES];
 
 E NEARDATA int multi;
+E const char *multi_reason;
 E NEARDATA int nroom;
 E NEARDATA int nsubroom;
 E NEARDATA int occtime;