ByteVector performance problem with replace

[Nick Shaforostoff]

> With some ID3 tags that use the Unsynchronisation flag we had some performance problems. On a header around 4MB it took > 10min to read it. So we came up with the following patch. Maybe some else is interested in this too.
on a side note: please note that the source file uses 2-space indentation style.

maybe we should add a corresponding config line to the text files so that editors adapt automatically their settings...
http://docs.kde.org/stable/en/kdesdk/kate/config-variables.html