Fix make test warning on Debian
TS-2736: Add static_cast
TS-2766: HdrHeap::coalesce_str_heaps doesn't properly calculate new heap size
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/trafficserver
TS-2766: HdrHeap::coalesce_str_heaps doesn't properly calculate new heap size