Feature request: allow to fetch photos of users other than current

[RKushnir]

Allow to pass user_id to Users#user_photos, like in other methods(e.g. user_friends).

[timych]

For now, only USER_ID = self is supported by users/photos API endpoint

[RKushnir]

The documentation doesn't reflect the actual state. I just tried in apigee console and it worked for non-self user id(e.g. https://api.foursquare.com/v2/users/34751494/photos?v=20131016)

In their API Explorer it works as well.