updated changelog according to hotfix release 0.39.2
fix sigar usage while testing
Merge pull request #936 from crate/m/fix_sigar_test_usage

fix sigar usage while testing
adapt TestSysNodesExpressions to new used expression
apply proper quoting to crash arguments
cache parsed sql statements
test for bytesref stubstring function
use substring(BytesRef) in SubstrFunction
Merge pull request #920 from crate/dobe-bytesrefsubstr

test for bytesref stubstring function
fix concurrency deadlocks