Implement/verify PAL aspect ratio correction

[Screwtapello]

From tepples on SNESdev:

Unlike the exact rational PAR of NTSC, the exact PAR of 50 Hz PAL involves some fairly big prime numbers such as 64489. This gives the fraction 2950000:2128137 ≈ 1.3862, and the unwieldiness of this is why I waited so long before establishing a 50 Hz counterpart to my long-running list of dot clock rates in 60 Hz picture generators.

Perhaps the most useful fractional approximation of the pixel aspect ratio of a PAL NES or PAL Super NES is 18:13 ≈ 1.3846. (I used 11:8 = 1.375 in the Linearity pattern of 240p Test Suite because I needed either the numerator or denominator to be 8, the width in pixels of a tile column or height in scanlines of a tile row.) The 18:13 ratio lends itself to using 52x72 DPI for preview in paint programs, such as GIMP with "Dot for Dot" turned off.

bsnes doesn't have a lot of love for PAL console emulation because (I think) Near never owned a PAL SNES to test with. However, it shouldn't be too hard to plug these numbers into bsnes somewhere.