Fix option modification by accident in primdec.lib

Hello,


this is a  proposal for eliminating accidental option modifications by 'primdec.ib'.
( http://www.singular.uni-kl.de:8002/trac/ticket/529 )

```
minAssPrimes, 
algeDeco,
splitCharp, 
minAssPrimesold,
newDecompStep 
```
needs a positive review related to changed option handling before merging.


Thanks,


Jakob