Pull term references out of xdrawcursor

Gradually reducing x.c dependency on Term object.  Old and new cursor
glyph/position are passed to xdrawcursor.  (There may be an opportunity
to refactor further if we can unify "clear old cursor" and "draw new
cursor" functionality.)

Signed-off-by: Devin J. Pohly <djpohly@gmail.com>

win.h

@@ -25,7 +25,7 @@ enum win_mode {
 
 void xbell(void);
 void xclipcopy(void);
-void xdrawcursor(void);
+void xdrawcursor(int, int, Glyph, int, int, Glyph);
 void xdrawline(Line, int, int, int);
 void xhints(void);
 void xfinishdraw(void);