Benchmark disabling USE_DSTRING or identify other unique selling point

[tautschnig]

It is not clear whether disabling USE_DSTRING actually adds value, or mainly had historic value. Benchmarking needs to be performed, unless there are other reasons to keep it, which are unknown to me.

[martin-cs]

For the general record ... My understanding of dstring is that we have a lot of string constants and perform a lot of comparisons of them and profiling highlighted the cost of these, so Daniel implemented a custom string class to reduce the overhead to comparing integers. It would be interesting to see if this is still the case.