Whoosh had a default setting for its index directory that was computed

at module initialization time. In unit tests, this resulted in the local

directory being used and not the directory set up for unit test state.
The Whoosh settings are now computed dynamically in order to take that

setting into account. On top of this, we also now override the path

hard-coded in settings.py (as part of the default Haystack

configuration, which is required) to also use the temporary storage

path.

Unit tests pass on Django 1.6 and 1.11.
Verified that a search-index directory was no longer being created

in the source directory.