MapDBLog: Enadling mmap file support (if platform supports it. currently only su…

…pported on 64bit JVMs). Fixes a problem described here: http://tinyurl.com/klgc36c

@@ -52,6 +52,7 @@ public class MapDBLog implements Log {
     public void open() throws IOException {
         txMaker = DBMaker
                 .newFileDB(dbFile)
+                .mmapFileEnableIfSupported()
                 .cacheSize(cacheSize)
                 .makeTxMaker();
     }