memory copy ---- void ColumnString::Append(ColumnRef column)

[1261385937]

The void ColumnString::Append(ColumnRef column) also has memory copy
BTW , In my scenario, the given column data (huge) will be no useful after calling this interface.
Here is a complicated inherit. If i make a overload interface, will be a lot of modification.

@Enmk , any suggest ?
I will submit a PR this weekend.

[Enmk]

Addressed in https://github.com/ClickHouse/clickhouse-cpp/pull/212