What is this socket?

[Anthony Lieuallen <just.an@xxxxxxxxxxx>]

My new apartment has a built-in heater/ac unit.  I'd like to build a
primitive thermostat for it (keep it off during the day, but on in time
for me to get home from work, etc), like I did with the window units in
my old apartment with X10.

But I have no idea what this is or how to deal with it:
plug:   http://img57.imageshack.us/my.php?image=plught2.jpg
socket: http://img225.imageshack.us/my.php?image=sockethk7.jpg

It looks like a standard US 3 prong plug, except one of the prongs is
rotated 90 degrees.  I measured the voltage at the socket at 214V AC.
Can anybody offer some pointers about what this socket is, and which /
if I can get an X10 module to control it?