[1.9.x] Fixed #25807 -- Instructed the migration writer about lazy objects.

Thanks to Trac alias mrgaolei for the report, Baptiste for the confirmation
and Tim for the review.

Backport of cc2ca9c550 from master

docs/releases/1.9.txt

@@ -448,7 +448,8 @@ Migrations
   :djadminopt:`migrate --fake-initial <--fake-initial>` to more easily detect
   initial migrations.
 
-* Added support for serialization of ``functools.partial`` objects.
+* Added support for serialization of ``functools.partial`` and ``LazyObject``
+  instances.
 
 * When supplying ``None`` as a value in :setting:`MIGRATION_MODULES`, Django
   will consider the app an app without migrations.

docs/topics/migrations.txt

@@ -659,6 +659,7 @@ Django can serialize the following:
 - ``decimal.Decimal`` instances
 - ``functools.partial`` instances which have serializable ``func``, ``args``,
   and ``keywords`` values.
+- ``LazyObject`` instances which wrap a serializable value.
 - Any Django field
 - Any function or method reference (e.g. ``datetime.datetime.today``) (must be in module's top-level scope)
 - Any class reference (must be in module's top-level scope)
@@ -666,7 +667,8 @@ Django can serialize the following:
 
 .. versionchanged:: 1.9
 
-    Serialization support for `functools.partial` was added.
+    Serialization support for ``functools.partial`` and ``LazyObject``
+    instances was added.
 
 Django can serialize the following on Python 3 only: