Added src/Makevars to .gitignore
Merge branch 'master' of https://github.com/stewid/git2r

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Added slot path to git_repository

Ongoing work to remove the usage of external pointers and instead only
keep the path to the repository.

* Replaced the the external pointer repo to a git repository with the
  path to a git repository.

* Removed the the external pointer to a git_revwalk.