New journal event "output"

Redundant information, but incredibly useful when you want to figure
out what happened without a (still nonexistent) journal replay tool.
The redundancy could help making a journal replay tool more robust.

To enable, set econfig key keep_journal to at least 2.  Output events
are *not* flushed to disk immediately.

include/types.h

@@ -48,6 +48,7 @@ struct nchrstr;
 struct nstr_item;
 struct nstr_sect;
 struct nukstr;
+struct player;
 struct plist;
 struct plnstr;
 struct range;