This method can be used to find multiple projects for multiple paths.
For example, take this snippet:

    Project.where_paths_in(%w{gitlab-org/gitlab-ce gitlab-org/gitlab-ee})

This will return an ActiveRecord::Relation containing the GitLab CE and
GitLab EE projects.

This method takes care of matching rows both case-sensitively and
case-insensitively where needed.

Project.find_with_namespace in turn has been modified to use
Project.where_paths_in without nuking any scoping (instead it uses
reorder(nil)). This means that any default scopes (e.g. those used for
"pending_delete" stay intact).

The method Project.where_paths_in was added so the various Markdown
filters can use a single query to grab all the projects referenced in a
set of documents, something Project.find_with_namespace didn't allow.