* closes #51 - > 1 month since notification * closes #61 - HBASE-18928 has already closed * closes #62 - HBASE-18929 has already closed * closes #67 - HBASE-19386 has already closed * closes #68 - HBASE-19387 has already closed Also adds a section to the committer guide in the reference guide about closing PRs. Signed-off-by: Mike Drob <mdrob@apache.org>