ARGB isn't saved correctly

[elronayellin]

Redirecting JuliaImages/ImageShow.jl#24 here.
It appears that save_ is first converting the input ARGB image to an RGBA image. The RGBA image bytes are used to create the CGBitmap, but the original ARGB channel ordering enumeration is passed in to CGBitmapContextCreate, so for example, red becomes blue.
It's not clear to me if the mapping from from ARGB to RGBA was intentional, ie, is the bug that it's mapped or that the wrong label is applied to the written data; it means save/load roundtrips wouldn't get you back to what you started with.