Fixed #24334 -- Allowed admin password reset to work with non-digit custom user model primary key.

Thanks Loic for help and Simon for review.

tests/auth_tests/urls_custom_user_admin.py

@@ -0,0 +1,21 @@
+from django.conf.urls import include, url
+from django.contrib import admin
+from django.contrib.auth import get_user_model
+from django.contrib.auth.admin import UserAdmin
+from django.contrib.auth.urls import urlpatterns
+
+site = admin.AdminSite(name='custom_user_admin')
+
+
+class CustomUserAdmin(UserAdmin):
+    def log_change(self, request, object, message):
+        # LogEntry.user column doesn't get altered to expect a UUID, so set an
+        # integer manually to avoid causing an error.
+        request.user.pk = 1
+        super(CustomUserAdmin, self).log_change(request, object, message)
+
+site.register(get_user_model(), CustomUserAdmin)
+
+urlpatterns += [
+    url(r'^admin/', include(site.urls)),
+]