root.wallpaper: Use main connection for pixmap filling (FS#1087)
Previously, cairo would often have to download the old wallpaper from the X11
server and then upload it again. It did this because it couldn't see that the
two X11 connections involved are actually connected to the same X11 server.
This commit fixes this by setting up the pixmap from our main X11 connection.
This is the same connection that we use for accessing the "old" wallpaper and
thus cairo doesn't have to do stupid things.
The big improvement with this is that this speeds up wallpaper setup a lot.
Signed-off-by: Uli Schlachter <psychon@znc.in>