OAK-1804: TarMK compaction

Automatically compress the compaction map data structure once every 100k entries.
Also only keep track of compacted nodes with at least two children.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1602256 13f79535-47bb-0310-9956-ffa450edef68
OAK-1804: TarMK compaction

Only use the compaction map to speed up equality checks of nodes and blobs, not those of all other records.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1602261 13f79535-47bb-0310-9956-ffa450edef68