Fixed #10161 -- Modified evaluation of query expressions to allow for...

Fixed #10161 -- Modified evaluation of query expressions to allow for operators that take the form of functions. This is mostly for the benefit of Oracle, but it should prove useful later on. Thanks to Ian for the report and feedback on the fix.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9898 bcc190cf-cafb-0310-a4f2-bffc1f526a37