Merge branch 'working_gitlab_url' into 'master'

Use a default for gitlab_url that usually works

This default lets gitlab-shell connect to Unicorn directly, instead of
going through Nginx. This has the following benefits:

- the majority of users no longer has to edit the `gitlab_url`;
- avoid issues when the external GitLab web address does not resolve on
  the GitLab server itself;
- avoid SSL certificate issues.

See merge request !32

config.yml.example

@@ -2,7 +2,11 @@
 user: git
 
 # Url to gitlab instance. Used for api calls. Should end with a slash.
-gitlab_url: "http://localhost/"
+# Default: http://localhost:8080/
+# You only have to change the default if you have configured Unicorn
+# to listen on a custom port, or if you have configured Unicorn to
+# only listen on a Unix domain socket.
+gitlab_url: "http://localhost:8080/"
 
 http_settings:
 #  user: someone