signed dvi/mdi are broken

[hellige]

Tested in goforth: http://0x10co.de/hiwhx Try typing: -50 5 / . 50 -5 / . The first results in -6564 and the second in -1. Both should be -10.

Try: -50 5 mod . 50 -5 mod . The first results in -2 and the second in 50. Both should be 0.

Here is a pure ASM test of DVI: http://0x10co.de/69nbr

[a1k0n]

fixed now with latest pull request.