fixing compilation errors in rot13_concise sample

* the function declarations where missing,
* det_index was spelt index_det
fix: solver_types/sudoku output 3x3 aligned

by accumulating the current row in the write_solution predicate,
and thus is aligned with the sudoku templates.
Merge branch 'fix-sudoku-grid' of https://github.com/sebgod/mercury into fix-sudoku-grid