close old db when rewriting

src/db.cpp

@@ -195,6 +195,7 @@ bool CDB::Rewrite(const string& strFile, const char* pszSkip)
                 bool fSuccess = true;
                 printf("Rewriting %s...\n", strFile.c_str());
                 string strFileRes = strFile + ".rewrite";
+                { // surround usage of db with extra {}
                     CDB db(strFile.c_str(), "r");
                     Db* pdbCopy = new Db(&dbenv, 0);
     
@@ -251,6 +252,7 @@ bool CDB::Rewrite(const string& strFile, const char* pszSkip)
                             fSuccess = false;
                         delete pdbCopy;
                     }
+                }
                 if (fSuccess)
                 {
                     Db dbA(&dbenv, 0);