Fix issue with date format for PHP 5.1.0+
Fix issue with date format for PHP 5.1.0+

As of PHP 5.1.0 the character 'o' represents the ISO-8601 year number in a date format. Therefore the 'o' needs to be escaped to avoid being converted to a year in the admin > configuration > system > long/short date format pulldown menu.

I should note that this fixes the issue for English, but you might want to consider moving the date format into a language string in order to provide better multi-language support.
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