Bug in reducedRowEchelonForm

[jchen419]

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The method reducedRowEchelonForm does not put identically zero rows at the bottom (and thus is technically not even in row echelon form, cf. here):

i1 : A = matrix{{0_(ZZ/2),0,0},{1,0,1},{0,1,1}}

o1 = | 0 0 0 |
     | 1 0 1 |
     | 0 1 1 |

             ZZ 3       ZZ 3
o1 : Matrix (--)  <--- (--)
              2          2

i2 : A == reducedRowEchelonForm A

o2 = true

Also, it would be nice for reducedRowEchelonForm to support more types of rings, e.g. cyclotomicFields from the Cyclotomic package, or more generally any output of toField.