misc: let views.py raise an ImportError if mellon is requested but unavailable

chrono/views.py

@@ -16,14 +16,15 @@
 
 import urllib
 
+from django.conf import settings
 from django.contrib.auth import logout as auth_logout
 from django.contrib.auth import views as auth_views
 from django.http import HttpResponseRedirect
 from django.shortcuts import resolve_url
 
-try:
+if 'mellon' in settings.INSTALLED_APPS:
     from mellon.utils import get_idps
-except ImportError:
+else:
     get_idps = lambda: []