Auto merge of #5232 - JohnTitor:git2-0.12, r=phansch
Auto merge of #5232 - JohnTitor:git2-0.12, r=phansch

Update git2 to 0.12

changelog: none

aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust