PostgreSQL, Fix change detection caused by wrong data for bytea unescaping.

This showed up when running BinaryTest#test_load_save with the more
restrictive input string handling of pg-0.18.0.pre20141117110243.gem .

Bytea values sent to the server are in binary format, but are
returned back as escaped text. To fulfill the assumption that
type_cast_from_database(type_cast_for_database(binary)) == binary
we unescape only, if the value was really received from the server.

activerecord/lib/active_record/connection_adapters/postgresql/oid/bytea.rb

@@ -5,6 +5,7 @@ module ActiveRecord
         class Bytea < Type::Binary # :nodoc:
           def type_cast_from_database(value)
             return if value.nil?
+            return value.to_s if value.is_a?(Type::Binary::Data)
             PGconn.unescape_bytea(super)
           end
         end

activerecord/test/cases/dirty_test.rb

@@ -688,7 +688,14 @@ class DirtyTest < ActiveRecord::TestCase
       serialize :data
     end
 
-    klass.create!(data: "foo")
+    binary = klass.create!(data: "\\\\foo")
+
+    assert_not binary.changed?
+
+    binary.data = binary.data.dup
+
+    assert_not binary.changed?
+
     binary = klass.last
 
     assert_not binary.changed?