the parameter to specify git tag is "git_tag"

The parameters description was referring to 'tag' but the actual name is 'git_tag'
Merge pull request #12 from spiddy/master

fixed documentation parameter name from 'tag'  to 'git_tag'
Fix creation of bare repository

If the repository is bare, it shouldn't checkout any branch, as this causes the following error:

```
err: /Stage[main]/Project/Git::Repo[project]/Exec[git_project_co_branch]/returns: change from notrun to 0 failed: /usr/bin/git checkout  returned 128 instead of one of [0] at .../puppet-git/manifests/repo.pp:90
```
Merge pull request #14 from leafac/patch-1

Fix creation of bare repository
Merge branch 'master' of git://github.com/nesi/puppet-git
Adding gentoo support