Fixes incompatibility with an Arch update by foregrounding cdm's call to startx

After an arch update, backgrounding the call to startx no longer worked. This
problem is referenced in the Arch Linux forums:
https://bbs.archlinux.org/viewtopic.php?pid=1413023
Updates cdm's call to startx to be compatible with Xorg 1.16.

In the Xorg 1.16 notes at:

  https://www.archlinux.org/news/xorg-server-116-is-now-available/

it mentions that X "must be launched from the same virtual terminal as was used
to log in"; therefore, cdm now launches, by default, on the same VT.

"...redirecting stderr also breaks rootless login"; therefore, cdm no longer
saves stderr. All the Xorg output should be available in is already available in
logs:

  ~/.local/share/xorg/