allow disabling object store write check

[icewind1991]

trafficstars

In clustered setups replication delay means that trying to read the object directly after writing it can fail.

This allows disabling the check by setting 'validateWrites' => false under the object store arguments in config.php

[PVince81]

so disabling it by default might cause problems in some scenarios ?

[PVince81]

/rebase

[blizzz]

/rebase

[skjnldsv]

/rebase