[1.2.X] Fixed #15175 -- Ensured that Chliean RUT checksum letters aren't case...

[1.2.X] Fixed #15175 -- Ensured that Chliean RUT checksum letters aren't case sensitive. Thanks to rvimer for the report, and to ersame for the patch.

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Backport of r15450 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15454 bcc190cf-cafb-0310-a4f2-bffc1f526a37