Fix GetChanges issue with changes in both sides#600

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dpordomingo wants to merge 3 commits intosrc-d:masterfrom dpordomingo:get-changes-go-git

+598-49

Commits on Mar 19, 2019

Add a failing test of analyzing PR with changes in both base and candidate
dpordomingo
committed
Add 'Three dots' feature in 'GetChanges' as default
dpordomingo
committed

Commits on Mar 25, 2019

WIP. Add vendored things
dpordomingo
committed