- The emulated vga card issues a dimension_update() using the real
screen dimensions and the real font height.
- The gui selects a font with the requested height or it recalculates
the screen height if the font height is not available.
- The text_update() function uses a new variable 'ncols' instead of the
fixed value of 80 for the number of text columns.
I have tested the changes with X11/Linux, SDL, wxGTK and win32. The changes
in the other guis are not tested yet.
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