Change the MySQL collation type to utf8_bin to ensure case-sensitive tags are supported

db/migrate/20150425164646_gitlab_change_collation_for_tag_names.acts_as_taggable_on_engine.rb

+# This migration is a duplicate of 20150425164651_change_collation_for_tag_names.acts_as_taggable_on_engine.rb
+# It shold be applied before the index additions to ensure that `name` is case sensitive.
+
+class GitlabChangeCollationForTagNames < ActiveRecord::Migration
+  def up
+    if ActsAsTaggableOn::Utils.using_mysql?
+      execute("ALTER TABLE tags MODIFY name varchar(255) CHARACTER SET utf8 COLLATE utf8_bin;")
+    end
+  end
+end