Modify proto with ChangeRequest.TwoDotsMode

[dpordomingo]

blocks src-d/lookout#530

In order to show the same changes than appear in Changes tab from GitHub PRs, the standard behavior for DataService.GetChanges is returning the changes as if doing git diff base...head (what works as git diff $(git merge-base base head) head)

If the analyzer wants all changes between base and head, (as done by git diff base..head) it must send TwoDotsMode as true in the ChangesRequest.

[carlosms]

👍

But let's wait for src-d/lookout#530 to be finished before we merge and release this one.

[dpordomingo]

It would be great if we could release this before merging src-d/lookout#530 to see Travis pass 💃
I know that if we merge this before the other, the analyzers will still having the same bug that previously, but since it's its current behavior... wdyt?

[carlosms]

Sorry, I didn't mean to merge src-d/lookout#530 before this one. What I meant is to:

• Finish Fix GetChanges issue with changes in both sides lookout#530, all reviewers approve, tests pass, etc.
• Merge this one, release new lookout-sdk
• Apply newer release on Fix GetChanges issue with changes in both sides lookout#530, then merge it.