fix GetUnit: it should return -1 for negative numbers
add view functions to investigate matrix entries
use vview
rename unit -> one and add IsOne
fix hnf to work in Z, Z/nZ
Contntt and remove content
simplify, Trace, Norm, various
ref counting for orders
basically n_Z (rintegers) using small immediate integers as in n_Q
works mainly.
 Known problems:
   memory corruption:
     bigintmat b[3][3];
     int i,j;
     for(i=1; i<=3; i++) {
       for(j=1; j<=3; j++) {
         b[i,j] = random(1, 2^29);};}; b;
      hnf(b);
    clapsing incomplete
make coeffs_BIGINT of type n_Z instead of n_Q