* Specify a line height for the default fx-CG 50 font so that the height
returned by dsize() is correctly 9, not 11.
* Adjust vertical and horizontal alignment in dtext_opt() and
dprint_opt() by a full pixel (DTEXT_BOTTOM, DTEXT_RIGHT) and half a
pixel (DTEXT_MIDDLE, DTEXT_CENTER) to make sure that the specified
position is within rendered text (as in DTEXT_LEFT and TEXT_TOP) and
to improve centering of strings with odd width or odd height, for
which there is only one valid position.