OAK-1660 - SegmentMK: Optimize reading of large binaries

Merge adjacent block records into one big block when reading

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1583880 13f79535-47bb-0310-9956-ffa450edef68
OAK-1660 - SegmentMK: Optimize reading of large binaries

Some further improvements

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1583881 13f79535-47bb-0310-9956-ffa450edef68
OAK-631: SegmentMK: Implement garbage collection

Improved flushing of the tar writer

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1583882 13f79535-47bb-0310-9956-ffa450edef68