Overhauled multi_throttling_server and multi_throttling_client logic.
Revert "Overhauled multi_throttling_server and multi_throttling_client logic."
Committed to wrong branch.

This reverts commit 030b06041a78ad7368f9a67a01d9b64593112006.
Merge branch 'next' of github.com:rethinkdb/rethinkdb into next