Fix multiprocessing regression in update_index
Fix multiprocessing regression in update_index

4e1e2e1c5df1ed1c5432b9d26fcb9dc1abab71f4 introduced a bug because it
used a property name which exists on haystack.ConnectionHandler but not
the Django ConnectionHandler class it's modeled on. Long-term, we should
rename the Haystack class to something like `SearchConnectionHandler`
to avoid future confusion.

Closes #1449

sgaist/django-haystack,barseghyanartur/django-haystack,barseghyanartur/django-haystack,barseghyanartur/django-haystack,sgaist/django-haystack,celerityweb/django-haystack,sgaist/django-haystack,celerityweb/django-haystack,celerityweb/django-haystack