Simple: Fix bug in score field collision

Previous commit 0a9c919 broke the simple backend for models that
didn't have an indexed score field.  Added a test to cover regression.
Set zip_safe in setup.py to prevent egg creation.

This is a work around for a bug in Django that prevents detection of management commands embedded in packages installed as setuptools eggs.
Merge pull request #752 from bigjust/master

Fix Simple Score field collision
Add preceding dots to hyperlink target; fixes issue 754.

This error was introduced in commit faacbcb.
Merge pull request #755 from toastdriven/issue/754-doc-build-warning

Docs: fix SearchQuerySet API link in tutorial

Thanks @benspaulding for the patch