Bugfix with dual method in ToricVectorBundles

[sashahbc]

Fixing a bug in ToricVectorBundles with the dual method, as well as a change to the corresponding test which was incorrect mathematically. For example, the dual of O(1) ++ O(-3) on the projective line should be O(-1) ++ O(3).
Before:

i2 : F = projectiveSpaceFan 1;

i3 : T = weilToCartier({1,0},F) ++ weilToCartier({0,-3},F);

i4 : T#"filtrationMatricesTable" -- here is the table for O(1) ++ O(-3)

o4 = HashTable{| -1 | => | -1 0 |}
               | 1 | => | 0 3 |

o4 : HashTable

i5 : Tv = dual T;

i6 : Tv#"filtrationMatricesTable" -- this is the table for O(-1) ++ O(1), not the correct dual

o6 = HashTable{| -1 | => | 1 0 |}
               | 1 | => | 0 -1 |

o6 : HashTable

After:

i2 : F = projectiveSpaceFan 1;

i3 : T = weilToCartier({1,0},F) ++ weilToCartier({0,-3},F);

i4 : Tv = dual T;

i5 : Tv#"filtrationMatricesTable" -- this is the correct table

o5 = HashTable{| -1 | => | 1 0 |}
               | 1 | => | 0 -3 |

o5 : HashTable

[nilten]

Sasha discussed this change with me and I approve it.

[mahrud]

Thanks!