Fix argument to header_encoding for PySVN.
Fix argument to header_encoding for PySVN.

Apparently PySVN doesn't understand the string 'utf-8', and instead requires
'UTF-8'. This is completely undocumented, but a helpful user discovered the
issue and suggested the fix. Trivial change.

reviewboard/reviewboard,bkochendorfer/reviewboard,beol/reviewboard,sgallagher/reviewboard,davidt/reviewboard,1tush/reviewboard,beol/reviewboard,chipx86/reviewboard,bkochendorfer/reviewboard,bkochendorfer/reviewboard,sgallagher/reviewboard,reviewboard/reviewboard,brennie/reviewboard,davidt/reviewboard,custode/reviewboard,1tush/reviewboard,beol/reviewboard,KnowNo/reviewboard,brennie/reviewboard,davidt/reviewboard,sgallagher/reviewboard,reviewboard/reviewboard,custode/reviewboard,bkochendorfer/reviewboard,custode/reviewboard,1tush/reviewboard,chipx86/reviewboard,1tush/reviewboard,brennie/reviewboard,1tush/reviewboard,KnowNo/reviewboard,1tush/reviewboard,custode/reviewboard,chipx86/reviewboard,1tush/reviewboard,reviewboard/reviewboard,brennie/reviewboard,1tush/reviewboard,1tush/reviewboard,beol/reviewboard,sgallagher/reviewboard,davidt/reviewboard,KnowNo/reviewboard,chipx86/reviewboard,KnowNo/reviewboard