[assembler] fixes system ctor trying to copy a per thread value
[elliptic-sipdg-discretization] readd current_grid_width()
- without it, compiler complains about pure virtual function
[elliptic-sipdg-discretization] readd current_grid_width()
- without it, compiler complains about pure virtual function
[test.products_boundaryl2/elliptic] fix unsafe conversion warning