Add index on ci_commits.gl_project_id

Fixes #3086

db/migrate/20151016131433_add_ci_projects_gl_project_id_index.rb

+class AddCiProjectsGlProjectIdIndex < ActiveRecord::Migration
+  def change
+    add_index :ci_commits, :gl_project_id
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
-ActiveRecord::Schema.define(version: 20151008130321) do
+ActiveRecord::Schema.define(version: 20151016131433) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -130,6 +130,7 @@ ActiveRecord::Schema.define(version: 20151008130321) do
     t.integer  "gl_project_id"
   end
+  add_index "ci_commits", ["gl_project_id"], name: "index_ci_commits_on_gl_project_id", using: :btree
   add_index "ci_commits", ["project_id", "committed_at", "id"], name: "index_ci_commits_on_project_id_and_committed_at_and_id", using: :btree
   add_index "ci_commits", ["project_id", "committed_at"], name: "index_ci_commits_on_project_id_and_committed_at", using: :btree
   add_index "ci_commits", ["project_id", "sha"], name: "index_ci_commits_on_project_id_and_sha", using: :btree