Add new test - sudoku solver.

tests/sudoku_solver.exp

@@ -0,0 +1,19 @@
+3 0 6 5 0 8 4 0 0 
+5 2 0 0 0 0 0 0 0 
+0 8 7 0 0 0 0 3 1 
+0 0 3 0 1 0 0 8 0 
+9 0 0 8 6 3 0 0 5 
+0 5 0 0 9 0 6 0 0 
+1 3 0 0 0 0 2 5 0 
+0 0 0 0 0 0 0 7 4 
+0 0 5 2 0 6 3 0 0 
+=================
+3 1 6 5 7 8 4 9 2 
+5 2 9 1 3 4 7 6 8 
+4 8 7 6 2 9 5 3 1 
+2 6 3 4 1 5 9 8 7 
+9 7 4 8 6 3 1 2 5 
+8 5 1 7 9 2 6 4 3 
+1 3 8 9 4 7 2 5 6 
+6 9 2 3 5 1 8 7 4 
+7 4 5 2 8 6 3 1 9