Bump git2 and remove dependency on cmake

[jtgeibel]

The git2 crate has dropped its dependnecy on cmake and we can as
well.

[sgrif]

Excellent, cmake is the most common cause of build failures for me. I'm actually wondering if we should just drop git2 entirely and subshell out to git now that this is off the web server. The savings from being able to work with a shallow clone likely outweigh the cost of subshelling.

[sgrif]

@bors: r+

[bors]

📌 Commit 044d713 has been approved by sgrif

[bors]

🔒 Merge conflict

This pull request and the master branch diverged in a way that cannot be automatically merged. Please rebase on top of the latest master branch, and let the reviewer approve again.

How do I rebase?

Assuming self is your fork and upstream is this repository, you can resolve the conflict following these steps:

1. git checkout update/git2 (switch to your branch)
2. git fetch upstream master (retrieve the latest master)
3. git rebase upstream/master -p (rebase on top of it)
4. Follow the on-screen instruction to resolve conflicts (check git status if you got lost).
5. git push self update/git2 --force-with-lease (update this PR)

You may also read Git Rebasing to Resolve Conflicts by Drew Blessing for a short tutorial.

Please avoid the "Resolve conflicts" button on GitHub. It uses git merge instead of git rebase which makes the PR commit history more difficult to read.

Sometimes step 4 will complete without asking for resolution. This is usually due to difference between how Cargo.lock conflict is handled during merge and rebase. This is normal, and you should still perform step 5 to update this PR.

Error message

Auto-merging Cargo.toml
Auto-merging Cargo.lock
CONFLICT (content): Merge conflict in Cargo.lock
Automatic merge failed; fix conflicts and then commit the result.

[bors]

☔ The latest upstream changes (presumably #1664) made this pull request unmergeable. Please resolve the merge conflicts.

[jtgeibel]

Rebased to resolve merge conflicts.

@bors r+

[bors]

📌 Commit 7952d3e has been approved by jtgeibel

[bors]

⌛ Testing commit 7952d3e with merge c3a7e1d...

[bors]

☀️ Test successful - checks-travis
Approved by: jtgeibel
Pushing c3a7e1d to master...

[jtgeibel]

The savings from being able to work with a shallow clone likely outweigh the cost of subshelling.

I didn't realize that libgit2 doesn't support shallow clones. While it looks like newer versions of git support committing to a shallow clone, I don't think pushing from a shallow clone is supported yet: "It is unclear how "push into/from a shallow repo" should behave." (Documentation/technical/shallow.txt)