Fixed spelling of "consistent" in admin/options.py

This pull request fixes a typo in a comment in the admin/options.py file.

I checked just to make sure, <http://en.wiktionary.org/wiki/consistant>, consistant is listed as a common misspelling of consistent and searching for it in Google will correct it.

According to <https://docs.djangoproject.com/en/1.5/internals/contributing/writing-code/submitting-patches/#typo-fixes-and-trivial-documentation-changes> this does not need a ticket in Trac, but if you would like, I could make one.