Allow choosing only active threads source admin

boards/admin.py

@@ -5,7 +5,7 b' from django.contrib import admin'
 from django.utils.translation import ugettext_lazy as _
 from django.core.urlresolvers import reverse
 from boards.models import Post, Tag, Ban, Thread, Banner, Attachment, \
-        KeyPair, GlobalId, TagAlias
+        KeyPair, GlobalId, TagAlias, STATUS_ACTIVE
 from boards.models.source import ThreadSource
 
 
@@ -186,3 +186,8 b' class GlobalIdAdmin(admin.ModelAdmin):'
 class ThreadSourceAdmin(admin.ModelAdmin):
     search_fields = ('name', 'source')
 
+    def formfield_for_foreignkey(self, db_field, request, **kwargs):
+        if db_field.name == 'thread':
+            kwargs['queryset'] = Thread.objects.filter(status=STATUS_ACTIVE)
+        return super().formfield_for_foreignkey(db_field, request, **kwargs)
+