Replaced exact lookups of the empty string with isnull lookups in Oracle.  Fixes the testPreventDuplicateComments case.
Replaced exact lookups of the empty string with isnull lookups in Oracle.  Fixes the testPreventDuplicateComments case.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@8827 bcc190cf-cafb-0310-a4f2-bffc1f526a37

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extra : convert_revision : 89aec2547312b0b8a5e1b4b8901481f86a8efe0e

adieu/django-nonrel,heracek/django-nonrel,heracek/django-nonrel,adieu/django-nonrel,adieu/django-nonrel,heracek/django-nonrel