fixed some bugs for zero and unit ideal decomposition in primdec.lib

Here is a proposal for a partial fix of `primdec.lib`
for zero and unit ideal decomposition.


Not yet fixed routines are:
* equiRadical 
* equidim
* equidimMax 
* equidimMaxEHV 
* zerodec 
* absPrimdecGTZ

Comments/suggestions?