[dev] [st] border crop fix

St has a bug where characters are always cropped slightly off of the
bottom and right hand sides of the window. I suspect that this is
caused by st not taking into account the border when regenerates the
pixmap during a window resize event.

I've attached a patch that appears to solve the problem for me. I'm
not very experienced with Xlib or C, so hopefully it doesn't
inadvertently introduce some other bug.

Ing