FLUME-2548: Enable SSLv2Hello for Avro Source and NettyAvroRpcClient

(Hari Shreedharan via Jarek Jarcec Cecho)
FLUME-2549: Enable SSLv2Hello for HttpSource

(Hari Shreedharan via Jarek Jarcec Cecho)
FLUME-2551. Add dev-support directory to source tarball.
Update RELEASE-NOTES for 1.5.2
Update CHANGELOG for 1.5.2
Merge remote-tracking branch 'remotes/origin/trunk' into trunk