VERSA: Fix XGP underline rectangle placement.

The underline offset in XGP files is positive downwards (as opposed to
the baseline offset, which is positive upwards!), and the ending Y
position of the rectangle should be computed from the line width, not
just the current position.

src/dcp/versa.211

@@ -4658,7 +4658,6 @@ undera:	 setzi b,		;relative to zero
 	call xarg1s
 	 return
 	add b,x			;baseline
-	movn b,b
 	add b,xgp.y		;y top
 	call xarg2		;get length
 	 return
@@ -4670,13 +4669,12 @@ doundr:				;b=y down, x=one x (not current), y=width,
 	aos (p)			;if get this far, success
 	skipn outena
 	 return			;don't do anything if not outputing
-	movsi x,(x)
-	addi y,(b)		;
-	movsi y,(y)
-	movs  w,xgp.x
-	move  z,xgp.y
-	sub   z,basel
-	movsi z,(z)
+	movsi w,(w)		;to X
+	movsi x,(x)		;from X
+	move  z,b
+	add   z,y
+	movsi z,(z)		;to Y
+	movsi y,(b)		;from Y
 	call plot"drect		;"
 	return
 
@@ -4686,7 +4684,7 @@ undenw:	call xarg1
 undend:	 movei a,2
 	call xarg1s
 	 return
-	movn b,x
+	move b,x
 	add b,xgp.y
 	move x,stubit
 	move w,xgp.x