Keep sindex block when initiating post construction. Could help with #2087.
Merge branch 'daniel_2073' into daniel_2087
Merge branch 'next' into daniel_2087
Just added a TODO
Merge branch 'next' into daniel_2087
Assign new UUIDs to backfilled sindexes. Also updated a comment.
Fix backtraces containing r.row in JavaScript

Closes #2096
Review 1331 by @neumino
Detach first/last child moved in internal_node::level.
Merge branch 'next' into daniel_2087
Merge branch 'daniel_2073_2' into next
Merge branch 'next' into sam_multiple_index_writes