Fix missing attribute error in replacment find code

Whoops. Just introduced this when ensuring we look for both the packgae
in other repositories as well as any replacments.

Signed-off-by: Dan McGee <dan@archlinux.org>

packages/models.py

@@ -326,7 +326,8 @@ def replacements(self):
                 replaces__name=self.pkgname)
         if not self.arch.agnostic:
             # make sure we match architectures if possible
-            arches = self.pkg.applicable_arches()
+            arches = set(Arch.objects.filter(agnostic=True))
+            arches.add(self.arch)
             pkgs = pkgs.filter(arch__in=arches)
         return pkgs