[dvipdfmx] improving color stack in xdvipdfmx

[Shunsaku Hirata]

> What is with the resource management? I guess the packages will have
> to add the /ColorSpace to the page resources?

No, dvipdfmx will manage color space resources. No need for users to
manually add the /ColorSpace to the page resources.

> Or if xdvipdfmx wants to do the management, how can then be avoided
> that it clashes with other additions? E.g. tikz is adding this:
>
> <</pgfprgb[/Pattern/DeviceRGB]>>

I understand a clash can occur, but I think still there is a way to avoid
clashes. I will try implementing it later.


Thanks,
Sunsaku Hirata