revert could remove added file if it's already been committed

[zombiezen]

Steps to Reproduce

$ gg init
$ touch foo.txt
$ gg add foo.txt
$ gg commit -m "initial commit"
$ touch bar.txt
$ gg add bar.txt
$ gg commit -m "added bar"
$ gg revert -r HEAD~ bar.txt

Expected Behavior

bar.txt is removed from the working copy and the index.

Actual Behavior

bar.txt is removed from the index, but not the working copy. This is fine, since it does not lose any data, but it would be fine to remove it from the working copy.

Version Info

gg built from source at 1ff07cfca9c38805dffd700cb665273f64b62181 on 2018-07-12T22:34:36Z
go: go1.10.3 gc linux/amd64
git version 2.18.0