L10n decorator doesn't respect a ModelAdmin's pre existing 'exclude' field

[mwesterhof]

as seen in the following 2 line of code from L10n:

    # hide added fields from form and admin
    cls.exclude = added_fields

L10n uses the exclude field to hide the added fields from the admin. This seems to completely overwrite any pre existing value. When the decorator is applied to a ModelAdmin with a customized exclude field, this creates problems for obvious reasons.