Some Corrections on PrimaryDecomposition.

Works now for the ideal given in example.g:
Q := HomalgFieldOfRationalsInSingular( );
A := Q * "x,y,z";
I := LeftSubmodule( "x^3-x, y*x^2-y,y^2-x^2,z-x*y", A );
Merge pull request #8 from HemEM/master

Some Corrections on PrimaryDecomposition.