Revert "fix removed keys handling"

This reverts commit 1eaee0b74f9a868c860905181e3848f014602401.
Revert "view changes: handle case where the doc is deleted"

This reverts commit 71654af7cdd514ee6c11d2721b3397a92bd27146.
Revert "fix: log removed keys"

This reverts commit 44a61c32f20512880e081b43c5dedf68a88cf75e.
Add rev to view changes respose

Conflicts:
	src/couch_mrview_updater.erl
Make they key-by-key-and-seq view btree optional independently of the key-by-seq view btree

Conflicts:
	src/couch_mrview.erl
	src/couch_mrview_compactor.erl
	src/couch_mrview_util.erl
Clean up update_log function for readability
Fix removal of keys from view seq index
Make view sig backwards compatible
Fix process_doc for temp views
fix first-pass log key addition and seq tree row removal
make REM_VAL an atom in order to differentiate between possible emitted values and the key-removed placeholder.
fix removal of duplicate keys from seq tree
Fix seqs in mrview updater

This commit makes it so the correct seqs are inserted into the mrview
sequence tree. It also fixes the btree comparison function for that
tree.
Update expected return of couch_mrview_util:get_view
keyseq_indexed is true by default if we index by sequence

don't break rcouch view changes behavior, where we expect to be able to index
by key.
fix view changes. make sure unittessts pass.