Add double width/height support. This passes all the relevant parts of

vttest apart from the "mad programmer" screen, which I think is a linedraw
problem.
This also intorduces proper clipping of the drawn text for good measure.

[originally from svn r2593]

mac/mac.h

@@ -59,6 +59,12 @@ typedef struct Session {
     int			font_ascent;
     int			font_leading;
     int			font_boldadjust;
+    Point		font_stdnumer;
+    Point		font_stddenom;
+    Point		font_widenumer;
+    Point		font_widedenom;
+    Point		font_bignumer;
+    Point		font_bigdenom;
     WindowPtr		window;
     WindowPtr		settings_window;
     PaletteHandle	palette;