R1:d3b8389256d3

include revision id in getdiff conduit call

Summary:
we need to know the revision id in order to generate
differential links. It would be amazing if there existed some library
for object <-> network call mapping, and we could get all the
information about an object given some unique ID rather than having to
create a dictionary manually. One can dream...

Test Plan:
1. setup on test phabricator instance
2. called differential.getdiff from client code with a valid diffid
3. verified that the correct…