Startup script not working

[Jesse Sheidlower <jester@panix.com>]

I'm running Xfce under wheezy on a desktop system. I have two monitors
permanently attached to the computer; that is, I never need to do any
configuration on the fly.

To set up dual-head, I run the simple command 

  xrandr --output HDMI2 --right-of HDMI1

I'd like to run this automatically at boot, and, following some
instructions I found online, I put this line in a file called
"45custom_xrandr" and put it in /etc/X11/Xsession.d/ However, this
doesn't get executed at boot, so I have to run the xrandr command
manually. Permissions are the same as the other files in that directory.
What do I need to do to get this to work?

I always screw things up when I make an xorg.conf file, so I'd prefer to
do this using xrandr, which always works fine, rather than writing an
xorg.conf. 

Thanks.