LearnBoost/stylus — pull request #1792 by maranomynet (2014-12-29 10:50:35+00:00)
Title: mix() BIF is broken for differently transparent colors

output alpha was calculated based on color1 only - leading to no alpha-channel mixing at all.

Example of old broken behavior:

```stylus
body
foo: mix( #000, rgba(#000,0.6) );
bar: mix( rgba(#000,0.6), #000 );
baz: mix( rgba(#000, 0.6), #000, 25% );
```

outputs:

```css
body {
foo: #000;
bar: rgba(0,0,0, 0.6);
baz: rgba(0,0,0, 0.6);
}
```

but should be (and is with this PR):

```css
body {
foo: rgba(0,0,0, 0.8);
bar: rgba(0,0,0, 0.8);
baz: rgba(0,0,0, 0.9);
}
```