[Xy-pic] Vertical alignment in xymatrix

[Michael Abbott]

> Instead of this:
> 	\xymatrix{-^X \ar[r] & -_X}
> you do this:
> 	\xymatrix{-^X_{\phantom{X}} \ar[r] & -_X^{\phantom{X}}}

Heh.  Eww.

I'm hoping that the developers have a cleaner solution :)