RRXinerama and rootless is not working properly

[uli42]

1. nxagent -ac -R :55
2. DISPLAY=:55 xrandr will show a list of resolutions not prefixed with nx which means rrxinerama is not active
3. pkill -HUP nxagent && sleep 3 && pkill -HUP nxagent
4. DISPLAY=:55 xrandr will show one resolution prefixed with nx which means rrxinerama is active

As rrxinerama is enabled by default but not active before the first screen resize. In rootless mode this normally never happens. With one exception: reconnect. So, two possible solutions:

1. trigger a (dummy) resize event in rootless mode after startup
2. never activate rrxinerama in rootless mode

[uli42]

additional observation: If you do the same without -R the nxagent will come up after pkill with a grey background instead of black as before the pkill (see #733)