_replicator docs should include the additional info from _active_tasks

There are some nice replication stats at /_active_tasks. I think that these should be exposed in the corresponding /_replicator documents (well, at least the first 3):
{
"doc_write_failures": 0,
"docs_read": 0,
"docs_written": 0,
"updated_on": 1322521694,
"started_on": 1322521569
}
This would make it easier to map a replication doc to its status.
This would benefit Futon, which currently seems to have only a limited interface to /_active_tasks.
This would bring _replicator closer to the old _replicate API, which returns the stats after one-time replication:
{
"ok": true,
"no_changes": true,
"session_id": "6647e26bc340b706bcf8f3c1ca709846",
"source_last_seq": 95,
"replication_id_version": 2,
"history": [

{ "session_id": "6647e26bc340b706bcf8f3c1ca709846", "start_time": "Mon, 28 Nov 2011 23:44:28 GMT", "end_time": "Mon, 28 Nov 2011 23:44:33 GMT", "start_last_seq": 0, "end_last_seq": 95, "recorded_seq": 95, "missing_checked": 24, "missing_found": 24, "docs_read": 24, "docs_written": 24, "doc_write_failures": 0 }

]
}