* [feature] Federate interaction policies + Accepts; enforce policies
* use Acceptable type
* fix index
* remove appendIRIStrs
* add GetAccept federatingdb function
* lock on object IRI
* update activity library so dereferencer returns full response and checks *final* link to allow for redirects
* temporarily add bodged fixed library
* remove unused code
* update getAccountFeatured() to use dereferenceCollectionPage()
* make sure to release map
* perform a 2nd decode to ensure reader is empty after primary decode
* add comment explaining choice of using Decode() instead of Unmarshal()
* update embedded activity library to latest matching https://github.com/superseriousbusiness/activity/pull/21
* add checks to look for changed URI and re-check database if redirected
* update max iteration count to 512, add checks during dereferenceAncestors() for indirect URLs
* remove doubled-up code
* fix use of status instead of current
* use URIs for checking equality for security
* use the latest known URI for boost_of_uri in case original was an indirect
* add dereferenceCollection() function for dereferenceAccountFeatured()
* pull in latest github.com/superseriousbusiness/activity version (and remove the bodge!!)
* fix typo in code comments
* update decodeType() to accept a readcloser and handle body closing
* switch to checking using BoostOfID and add note why not using BoostOfURI
* ensure InReplyTo gets unset when deleting status parent in case currently stubbed
* add tests for Collection and CollectionPage iterators
* some small code fixups and changes
* add check in ResolveIncomingActivity for transient activity types (i.e. activity ID is nil)
* update test to handle new transient behaviour
