FIX: Check against reserved usernames should be case insensitive.

app/models/user.rb

@@ -147,7 +147,9 @@ class User < ActiveRecord::Base
 
   def self.username_available?(username)
     lower = username.downcase
-    User.where(username_lower: lower).blank? && !SiteSetting.reserved_usernames.split("|").include?(username)
+
+    User.where(username_lower: lower).blank? &&
+      !SiteSetting.reserved_usernames.split("|").any? { |reserved| reserved.casecmp(username) == 0 }
   end
 
   def self.plugin_staff_user_custom_fields

spec/models/user_spec.rb

@@ -433,6 +433,14 @@ describe User do
     it 'returns false when a username is taken' do
       expect(User.username_available?(Fabricate(:user).username)).to eq(false)
     end
+
+    it 'returns false when a username is reserved' do
+      SiteSetting.reserved_usernames = 'test|donkey'
+
+      expect(User.username_available?('donkey')).to eq(false)
+      expect(User.username_available?('DonKey')).to eq(false)
+      expect(User.username_available?('test')).to eq(false)
+    end
   end
 
   describe 'email_validator' do