Destroy kv_location before waiting for the superblock to be returned in erase_small_range. Closes #3455.
Revert "Destroy kv_location before waiting for the superblock to be returned in erase_small_range. Closes #3455."
Committed to 'next' by accident, sorry.

This reverts commit 47762c604a73f260bdec09b4b3af9ce22913ef32.
Destroy kv_location before waiting for the superblock to be returned in erase_small_range. Closes #3455.
Merge branch 'next' of github.com:rethinkdb/rethinkdb into next
Merge branch 'next' into daniel_3455
Added a warning to find_keyvalue_location_for_write about when the superblock promise is getting pulsed.
Merge branch 'next' into tim/config-status-porcelains