Add comments when you view the diff between two uploads of an MR

Issue idea came from: https://news.ycombinator.com/item?id=14353618 and https://gitlab.slack.com/archives/C0AR2KW4B/p1495020802277980

Problem

You can’t add comments when you view the diff between two uploads of an MR.

image

Proposal

  • Add ability to comment on diff of in-between-versions
  • Show in subdiscussion that this comment is on diff of in-between-versions

Related issues

CC/Call to actions

@markglenfletcher @victorwu (do we already have an issue for this?)