Merge remote-tracking branch 'upstream/master' into 0.5

issue=#null modify version 0.3.1 -> 0.3.2

modify version 0.4.1 -> 0.4.2

modify version from master -> 0.5.0

modify version 0.4.0 -> 0.4.1

issue=baidu#907 bugfix of replication sdk

Merge pull request baidu#863 from 00k/0.3

同步PR baidu#862 到0.3分支

set level0 sst file num to 2000

set level0 sst file num to 20

Merge pull request baidu#489 from xupeilin/find-zombie-ts

var name fix