Description of problem:
GETting a consumer--repo--distributor object from the Pulp REST API yields a JSON structure with wrong _href field e.g.:
  /pulp/api/v2/consumers/test_consumer/bindings/test_rpm_repo/test_distributor/test_consumer/test_rpm_repo/test_distributor/

Version-Release number of selected component (if applicable):
2.2

How reproducible:
Always

Steps to Reproduce:
1. create a repo, associate it with an yum-type importer and distributor
2. create a consumer
3. bind the consumer to the repo--distributor created
4. result: the binding object has invalid _href field
5. try following the invalid _href field
6. 404 response

Actual results:
_href field of a consumer--repo--distributor object is invalid

Expected results:
_href field of a consumer--repo--distributor object is correct

Additional info:
### Screen log

[mkovacik@malina pulp]$ http --verify=no -a admin:admin  https://pulp.example.com/pulp/api/v2/consumers/test_consumer/bindings/test_rpm_repo/test_distributor/
HTTP/1.1 200 OK
Content-Length: 692
Content-Type: application/json
Date: Tue, 15 Oct 2013 08:23:27 GMT
Server: Apache/2.4.6 (Fedora) OpenSSL/1.0.1e-fips mod_wsgi/3.4 Python/2.7.5

{
    "_href": "/pulp/api/v2/consumers/test_consumer/bindings/test_rpm_repo/test_distributor/test_consumer/test_rpm_repo/test_distributor/", 
    "_id": {
        "$oid": "525cfacec805d07f7010bb79"
    }, 
    "_ns": "consumer_bindings", 
    "binding_config": null, 
    "consumer_actions": [], 
    "consumer_id": "test_consumer", 
    "deleted": false, 
    "details": {
        "ca_cert": null, 
        "client_cert": null, 
        "gpg_keys": [], 
        "protocols": [
            "http", 
            "https"
        ], 
        "relative_path": "/pulp/repos//zoo/", 
        "repo_name": "test_rpm_repo", 
        "server_name": "pulp.example.com"
    }, 
    "distributor_id": "test_distributor", 
    "id": "525cfacec805d07f7010bb79", 
    "notify_agent": true, 
    "repo_id": "test_rpm_repo", 
    "type_id": "yum_distributor"
}

[mkovacik@malina pulp]$ http --verify=no -a admin:admin  https://pulp.example.com/pulp/api/v2/consumers/test_consumer/bindings/test_rpm_repo/test_distributor/test_consumer/test_rpm_repo/test_distributor/
HTTP/1.1 404 Not Found
Content-Length: 9
Content-Type: text/html; charset=UTF-8
Date: Tue, 15 Oct 2013 08:24:45 GMT
Server: Apache/2.4.6 (Fedora) OpenSSL/1.0.1e-fips mod_wsgi/3.4 Python/2.7.5

not found