db_lmdb: create all needed directories, not just the leaf one

src/blockchain_db/lmdb/db_lmdb.cpp

@@ -943,7 +943,7 @@ void BlockchainLMDB::open(const std::string& filename, const int mdb_flags)
   }
   else
   {
-    if (!boost::filesystem::create_directory(direc))
+    if (!boost::filesystem::create_directories(direc))
       throw0(DB_OPEN_FAILURE(std::string("Failed to create directory ").append(filename).c_str()));
   }