BUG: vnl_matrix move-assignment segfault

[drewgilliam]

In the move-assignment operator= for vnl_matrix (see PR #694) when both left-hand side and right-hand side objects manage their own memory, the right-hand side object should finally be invalidated with null data, zero size, and m_LetArrayManageMemory set to a default value of true (not false). The system segfaults should a user attempt to std::swap two matrices.

Set m_LetArrayManageMemory to true in move-assignment operator= for both vnl_matrix and vnl_vector. Add more swap tests, including native swap and std::swap for both vnl_matrix and vnl_vector.

More Details

During move-assignment, vnl_matrix wrongly reset m_LetArrayManageMemory to false. This is an issue should a user attempt to std:swap two matrices (while users should prefer the native vnl_matrix::swap function, std::swap should certainly not segfault).

The C++11 std::swap method is implemented as follows

template<typename T> void swap(T& t1, T& t2) {
    T temp = std::move(t1); // line (1)
    t1 = std::move(t2);     // line (2)
    t2 = std::move(temp);   // line (3)
}

When using std::swap on a vnl_matrix, matrix t1 would be cleared after line 1 but with m_LetArrayManageMemory = false. Line two would attempt to follow a code path for externally managed memory and the system would segfault.

PR Checklist

🚫 Makes breaking changes to the vxl/core/* API that requires semantic versioning increase
🚫 Makes design changes to existing vxl/core* API that requires semantic versioning increase
🚫 Makes changes to the contributed directory API DOES NOT require semantic versioning increase
✔️ Adds tests and baseline comparison (quantitative).
🚫 Adds Documentation.

[drewgilliam]

@hjmjohnson