Fix "ugly fades" bug. The border colour was rendered behind the fill colour...

Fix "ugly fades" bug. The border colour was rendered behind the fill colour unless both primary and secondary alpha were non-zero. The \fad and \fade tags both set \alpha rather than \1a \2a \3a \4a, and \alpha is a wholly separate alpha value which wasn't considered at all in this case.
Making it never draw the fill in border colour fixes this and doesn't seem to have any adverse effects.

Originally committed to SVN as r2276.