lol, how did it manage to work for years? (z1 - z2 * z.Round) shouldn't respect signs of z1 and z2. It turns out we often had arbitrary .Frac value in division result. Also fixes issue #613.

[patterns]
**.h = native
**.c = native
**.cpp = native
**.lua = native
**.txt = native
**.pas = native
**.inc = native
**.hs = native