Properly enclose 'model' in quotes when testing p.[attr]

This reverts commit 323405e6, reversing
changes made to 41a68dde.

SQL alchemy Unique validator allows multiple None values

Fix search input margin

Fix 'TypeError: descriptor 'lower' requires a 'str' object but received a 'unicode''

Fix small typo

Before: https://www.dropbox.com/s/ppif4opa904m91k/broken_search2.png

After: https://www.dropbox.com/s/bxy065pzch39bg1/broken_search.png

Currently, the margin of the search input messes up the border line.

Fix List.html Checkbox Width

Merge most recent changes

Add index page for clicking through examples.

Merge from central repo into bryhoyt's fork

Update 'Adding a new model backend' page.

File and ImageUploadField fixes

The issue at hand is in fact an error on import, and more specific exceptions are nicer to work with.