Fixes for win_ratio/aspect_ratio confusion. It was due to confusion in the

Fixes for win_ratio/aspect_ratio confusion.  It was due to confusion in the
meaning of "win_ratio".  I've removed win_ratio and added fov_ratio and
aspect_ratio, as it seems both are needed.

n.b. The multi-line changes in fgReshape comprise:
  extracting common code,
  removing an apparently arbitrary "+1" on the view height,
  changing "set_win_ratio" to "set_aspect_ratio".