cmd/geth, trie: report on trie cache unloads, also add debug log

trie/trie.go

@@ -47,6 +47,13 @@ func CacheMisses() int64 {
 	return cacheMissCounter.Count()
 }
 
+// CacheUnloads retrieves a global counter measuring the number of cache unloads
+// the trie did since process startup. This isn't useful for anything apart from
+// trie debugging purposes.
+func CacheUnloads() int64 {
+	return cacheUnloadCounter.Count()
+}
+
 func init() {
 	sha3.NewKeccak256().Sum(emptyState[:0])
 }