So what happened is that your character was facing along the positive Y axis. So when you rigged it up, you accidentally got the left and right sides switched. If the character imports into 3DXchange facing away from you, it is going to do that, unless you rotate it around.
I rotated the model 180 so it was facing forward (-Y) in 3DXchange, reset the transform, and then proceeded as normal. here is the fixed version.