Rounding the corners of the splash screen image according to the theme's roundness preference.
The rounding of the splash screen block itself depends on the wcol_menu_back.roundness theme settings, and user can even set it to zero.
So, in this case the splash image rounding will not match the block ones.
This patch allows you to add proper corner rounding when the image is displayed.
It process only the corner part of the image, both corners in one pass, so a small number of operations are performed.
It also makes it easier to create new splash images as there is no need to worry about adding corner rounding.
Splash screen screenshots: