Add support for ARGB visual when reparent window.

When reparent window, check whether the window to reparent has the depth
of 32. When that is true, we should create a parent window with the same
32bit depth. So the window with alpha channel will show as translucency,
or it will have a opaque background.
Slightly clean up ARGB support
Merge pull request #172

With some small stylistic changes