Merge branch 'git-worktree'

Closes #970

git/git.go

@@ -37,6 +37,15 @@ func Dir() (string, error) {
 }
 
 func HasFile(segments ...string) bool {
+	// The blessed way to resolve paths within git dir since Git 2.5.0
+	output, err := gitOutput("rev-parse", "-q", "--git-path", filepath.Join(segments...))
+	if err == nil && output[0] != "--git-path" {
+		if _, err := os.Stat(output[0]); err == nil {
+			return true
+		}
+	}
+
+	// Fallback for older git versions
 	dir, err := Dir()
 	if err != nil {
 		return false