Added dedicated Rake task for setting up Postgres

This ensures any PostgreSQL specific schema changes (e.g. expression
indexes) are created when setting up the database.

lib/tasks/gitlab/setup.rake

@@ -16,6 +16,7 @@ namespace :gitlab do
 
     Rake::Task["db:setup"].invoke
     Rake::Task["add_limits_mysql"].invoke
+    Rake::Task["setup_postgresql"].invoke
     Rake::Task["db:seed_fu"].invoke
   rescue Gitlab::TaskAbortedByUserError
     puts "Quitting...".red

lib/tasks/migrate/setup_postgresql.rake

@@ -0,0 +1,6 @@
+require Rails.root.join('db/migrate/20151007120511_namespaces_projects_path_lower_indexes')
+
+desc 'GitLab | Sets up PostgreSQL'
+task setup_postgresql: :environment do
+  NamespacesProjectsPathLowerIndexes.new.up
+end