Update check script in stable branch

* GitLab Shell 1.7.1 is required
* Global projects are not supported (refs #5152)

Fix API::MergeRequest in 6-1-stable

Refs #5145

Corrects the update document to match the version of gitshell specified ...

Added .ruby-version & .ruby-gemset in .gitignore

Drop support of root namespace in model

Don't show users password change page if ldap users

Corrects the update document to match the version of gitshell specified in the install document (1.7.1)

Fix issue_closing_regex in gitlab.yml.example

It turns out that regex escapes and YAML quoted-scalar escapes don't play
nicely together.

Update unicorn.rb.example

[WIP]Drop support of root namespace in routing

Add "public-project?" checkbox to new-project view 

Minor UI fix in views/public/project/index.html.haml

Fix typo in installation.md

Re-enable notifying commit authors of new commit notes