Transparent Window Support

One of the exciting features of skim 1.3.0 is demonstrated here: you can see that the input window (75% opacity) and main window (50% opacity) are all transparent (the main window is on the "Home Page" of the logo, not so obvious due to low opacity). Of course, you have to use xorg >= 6.8.0. The core support is finished in CVS, however the configure dialog is not yet implemented.