Django Evolution's modern JSON-based serializer gained support for

RENAMED_FIELD_TYPES, which allowed codebases to map legacy field

classes to new ones. However, the legacy pickle-based deserializer

didn't have this capability, meaning that older codebases would still

fail to find renamed modules.
This change adds support for RENAMED_FIELD_TYPES in the legacy

unpickler. This unpickler already hard-codes support for some legacy

types, making this pretty straightforward.

Tested an upgrade with the legacy unpickler referencing a module we

wanted to rename. Verified the upgrade worked successfully.