index: stores repository name as . and path as relative ./.git

```
$ ./bushi-index -t test-db.db -s .
repository: .
path:       ./.git
commits:    1117533
files:      116618
references: 151 (branches:17，tags:134)
```

When adding a repository using the current-directory shortcut `.`, the stored name and path are not normalized. Consider using `absolute_pathdup()` from git-internal?