split DUMPLOG

DUMPLOG requests the DUMPLOG feature as it does now
DUMPLOG_CORE requests the internal buffering only (used for CRASHREPORT)

This allows CRASHREPORT to access recent messages without performing
any file I/O.

src/save.c

@@ -1233,7 +1233,7 @@ freedynamicdata(void)
 #ifdef USER_SOUNDS
     release_sound_mappings();
 #endif
-#ifdef DUMPLOG
+#ifdef DUMPLOG_CORE
     dumplogfreemessages();
 #endif
     discard_gamelog();