fix mysql date and datetime type

Author: xucs007

source/ddbc/drivers/mysqlddbc.d

@@ -1085,9 +1085,7 @@ public:
             return 0;
         if (v.convertsTo!(long))
             return v.get!(long);
-	else if (v.convertsTo!(string))
-            return v.get!(string).to!long;
-        throw new SQLException("Cannot convert field " ~ to!string(columnIndex) ~ ": '" ~ v.toString() ~ "' to long. type=" ~ v.type.to!string);
+        throw new SQLException("Cannot convert field " ~ to!string(columnIndex) ~ ", " ~ metadata.getColumnName(columnIndex) ~ ": '" ~ v.toString() ~ "', to long. Its type=" ~ v.type.to!string);
     }
     override ulong getUlong(int columnIndex) {
         checkClosed();