Accept fractional values for CS variety margin

[frostburn]

gallium (futile to ping) — Today at 3:56 PM

The 'Constant structure / variety margin in cents' setting (in Analysis - More options) needs to allow fractions of a cent. SW tends to overestimate the MV in scales processed by the 'Modify scale - Temper' modal because some of the intervals then differ by a tiny decimal fraction of a cent due to the rounding (by 0.000001 in my case because I had 'Cents digits after decimal point' set to 6). Test: https://scaleworkshop.plainsound.org/scale/5Kld-nmmc
(I mean, 1c tolerance works for me, but that it can only be an integer number of cents is a strange restriction.)