#131 Assume that a scaler it compatible as long as it works

[Alberto Salvia Novella]

Right now Dosbox assumes that a scaler isn't good if it won't draw to the edge of the screen, and only will accept any other with the -forcescaler option.

By default Dosbox uses normal2x, but it will move to "none" if the above scenario happens. On modern screens that frequently leads to a blurry screen, versus it having small black edges.

The latest usually leads to better quality, sharper graphics, speciably noticeable in text:
https://imgur.com/a/oLeBSGK