Fix typo in the default encoding name
Fix typo in the default encoding name

The default encoding for repositories (if utf-8 fails) was `iso-5589-15`, which
isn't valid. The correct one is `iso-8859-15`.

Testing Done:
Encoding names were tested in the Python shell

Reviewed at https://reviews.reviewboard.org/r/6561/

KnowNo/reviewboard,brennie/reviewboard,custode/reviewboard,beol/reviewboard,reviewboard/reviewboard,KnowNo/reviewboard,beol/reviewboard,chipx86/reviewboard,davidt/reviewboard,custode/reviewboard,bkochendorfer/reviewboard,davidt/reviewboard,bkochendorfer/reviewboard,custode/reviewboard,bkochendorfer/reviewboard,KnowNo/reviewboard,chipx86/reviewboard,beol/reviewboard,reviewboard/reviewboard,sgallagher/reviewboard,chipx86/reviewboard,sgallagher/reviewboard,sgallagher/reviewboard,brennie/reviewboard,custode/reviewboard,chipx86/reviewboard,brennie/reviewboard,davidt/reviewboard,KnowNo/reviewboard,beol/reviewboard,davidt/reviewboard,brennie/reviewboard,bkochendorfer/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,sgallagher/reviewboard