clamav_to_yara.py creates lots of invalid jumps e.g. [4-4]

```
I've tried converting clamAV signature files to YARA but the converted yara 
file contain lots of invalid jumps like [4-4]. I've tried this on Windows 7 SP1 
x64 and Ubuntu 11.10 x64. The python version is 2.7. Yara version tried 1.5 and 
1.6. 


```

Original issue reported on code.google.com by `kola...@gmail.com` on 17 Nov 2011 at 8:41
