Upsert method

[leonardb]

Would love to see a utility method for handling upsert pattern and automated conflict resolution.
Feature should allow for 'partial update' of document. I know it's not part of the Couch API, but I think it's something that everyone finds to be an irritation and handling in the library would make life easier.

Upsert outline:
if duplicate key on insert, pull existing document with conflicting key, merge new document into existing document replacing existing values, save merged document and return with new _rev.

Auto conflict resolution:
if when saving, newer version exists (conflict), pull newer version of document, merge data from request into new document, save merged document and return new _rev

Partial update description:
given existing document in couchdb
{
"_id": "doc1",
"_rev": "AAA",
"type": "mytype",
"value": "ZZZ"
}

now we have the _id of that doc from a result set from a view, and just want to append a new property/attribute to the doc without having to jump through exception handling hoops in client code every time,

$update_doc = array("_id"=>"doc1","mynewfield"=>"mynewvalue");
$res = $conn->upsertDoc($update_doc);

we end up with
$res == array("ok"=>1, "id" => "doc1", "rev"=>"BBB");

and in couchdb:

{
  "_id": "doc1",
  "_rev": "BBB",
  "type": "mytype",
  "value": "ZZZ",
  "mynewfield": "mynewvalue"
}