couchstore compactor interleaves byseq btree nodes and doc bodies

(Assigning on Damien for initial prioritization)

Looks like my old finding is still valid. Number of page cache pages required to keep byseq index in ram is actually increasing after compactor.

That's because it saves by seq leaf node after it's data items.

I have tools and data that confirm my finding (real vbucket files from perf run).

When I told about this problem to Aaron prior to 2.0 he said it's going to be easy on afaik indexer branch. Looks like this branch is merged at last and it's time to reconsider.