Allow multisite sites to be passed into the URL resolution system of Core.
Allow multisite sites to be passed into the URL resolution system of Core.

This allows cross-site URL resolution when in multi-site mode.

nicholasryan/CorePlus,nicholasryan/CorePlus,nicholasryan/CorePlus,nicholasryan/CorePlus,nicholasryan/CorePlus,nicholasryan/CorePlus,nicholasryan/CorePlus,nicholasryan/CorePlus