Summary:
There were lots of small stupid mistakes with pushrebase replay in past.
Since pushrebase replay will stay with us for quite some time,
let's add a test to prevent these regressions in future.
In tests we'll use filesystem+sqlite instead of everstore + xdb to fetch
requests to replay.
Reviewed By: HarveyHunt
Differential Revision: D13940390
fbshipit-source-id: a4398d1c8c22bf16a85d6391a1f5665ce4b73eb1
