Added xcap-caps payload support

Ignore-this: 6e719634278004258474033149700af5

darcs-hash:20100810111748-1e3d8-e11b61b8ad2f745d8573b45cff453a88c4b5bdde
Added custom extension for extra attributes to entries in resource-lists

Ignore-this: efa9ebb0432607e0a1832404aebaaebf

darcs-hash:20100812110535-1e3d8-d0a2b261f2f132a866436c37477d5a90fd53e2d7