Support huge wallpapers and small request lengths.
Support huge wallpapers and small request lengths.

The X protocol has a limited request size. In default settings, it
could be around 16 MB, which is not enough if you have two outputs
with ultra hd resolutions.

Support splicing the resulting image into sub images before
transmission.

Signed-off-by: Tobias Stoeckmann <059b8b880f8441509ec8a65b50b4c6ae74ebea76@stoeckmann.org>

stoeckmann/xwallpaper,stoeckmann/xwallpaper