Commits discarded by history rewriting should be ignored and branch considered as new

[antoine-malliarakis]

Checklist

• [x] All new jobs, commands, executors, parameters have descriptions (not relevant here)
• [x] Examples have been added for any significant new features (not relevant here)
• [x] README has been updated, if necessary (not relevant here)

Motivation, issues

Behaviours in case of branch being rebased or when the job previous runs included entries on commit which had been discarded (following a rebase or a squash) was... not working.

This is basically what's being described in the 3 below issues:

• https://github.com/iynere/compare-url/issues/41
• https://github.com/iynere/compare-url/issues/40
• https://github.com/iynere/compare-url/issues/25

Description

Basically there was an issue which occurred with history rewrites (which can happen often in cases where people tend to squash their commits and / or rebase at head before merging, which is my case).

The idea is to basically say that:

• If a commit from a previous build was lost it should be ignored
• If a branch's previous job was on a no longer existing commit it should be considered as a new branch

[LoicEvenium]

This should fix #25 also I think