Quarantine removal

The following changes expand the removal of the quarantine metadata information.
On 10.10 and Xcode 6, it uses the new `NSURLQuarantinePropertiesKey` key, setting the value to `[NSNull null]` as recommended by the Apple docs.
Please reverse the if-else (and remove the else), and add min_required ifdefs, like so:

    + (void)releaseFromQuarantine:(NSString *)root
    {
    #if __MAC_OS_X_VERSION_MIN_REQUIRED < 101000
        if (!&NSURLQuarantinePropertiesKey) {
            // old code here
            return; // don't continue to the new code
        }
    #endif
        // new code here
    }