This is required in situations where autoCommit.openSearcher is set to "false",
and you don't want to rely on core restarts to make committed index updates available to new searches.
It's already configured like this in the Common Web Platform environments,
so this change will mainly affect other environments (such as Silverstripe Platform).
To opt out of this new behaviour, set up a custom solrconfig.xml.
More details in https://github.com/silverstripe/silverstripe-fulltextsearch/issues/274
Ingo Schommer
Andrew Aitken-Fincham