Use SDL_Pango to render text in SDL mode.
Set the font for the Pango renderer.
Remove friend declaration -- it's a struct.
Only use SDL_Pango if WITH_SDL_PANGO is set.

This will allow us to use SDL but without SDL_Pango on Win32, where we
plan to keep using the native font rendering.
Add comment about WITH_SDL_PANGO.

The option's there to turn it on in Win32, for the adventurous.
With Pango, try Arial first, then sans.
Hard-code Pango DPI to match Windows rendering.
Adjust masking for text edges in Pango.
Update copyright.