handle double pluralization for irregular plurals

[#6363]
Signed-off-by: NSantiago Pastorino <santiago@wyeworks.com>

activesupport/lib/active_support/inflections.rb

@@ -4,10 +4,12 @@ module ActiveSupport
     inflect.plural(/s$/i, 's')
     inflect.plural(/(ax|test)is$/i, '\1es')
     inflect.plural(/(octop|vir)us$/i, '\1i')
+    inflect.plural(/(octop|vir)i$/i, '\1i')
     inflect.plural(/(alias|status)$/i, '\1es')
     inflect.plural(/(bu)s$/i, '\1ses')
     inflect.plural(/(buffal|tomat)o$/i, '\1oes')
     inflect.plural(/([ti])um$/i, '\1a')
+    inflect.plural(/([ti])a$/i, '\1a')
     inflect.plural(/sis$/i, 'ses')
     inflect.plural(/(?:([^f])fe|([lr])f)$/i, '\1\2ves')
     inflect.plural(/(hive)$/i, '\1s')
@@ -15,7 +17,9 @@ module ActiveSupport
     inflect.plural(/(x|ch|ss|sh)$/i, '\1es')
     inflect.plural(/(matr|vert|ind)(?:ix|ex)$/i, '\1ices')
     inflect.plural(/([m|l])ouse$/i, '\1ice')
+    inflect.plural(/([m|l])ice$/i, '\1ice')
     inflect.plural(/^(ox)$/i, '\1en')
+    inflect.plural(/^(oxen)$/i, '\1')
     inflect.plural(/(quiz)$/i, '\1zes')
 
     inflect.singular(/s$/i, '')

activesupport/test/inflector_test.rb

@@ -63,6 +63,13 @@ def test_uncountable_word_is_not_greedy
       assert_equal(singular.capitalize, ActiveSupport::Inflector.singularize(plural.capitalize))
     end
   end
+  
+  SingularToPlural.each do |singular, plural|
+    define_method "test_pluralize_#{plural}" do
+      assert_equal(plural, ActiveSupport::Inflector.pluralize(plural))
+      assert_equal(plural.capitalize, ActiveSupport::Inflector.pluralize(plural.capitalize))
+    end
+  end
 
   def test_overwrite_previous_inflectors
     assert_equal("series", ActiveSupport::Inflector.singularize("series"))

activesupport/test/inflector_test_cases.rb

@@ -44,6 +44,7 @@ module InflectorTestCases
 
     "datum"       => "data",
     "medium"      => "media",
+    "stadium"     => "stadia",
     "analysis"    => "analyses",
 
     "node_child"  => "node_children",