Make M*LIB stricter for INIT_MOVE operator:

* either the default INIT_MOVE operator works ('=')
* either an INIT_MOVE method is defined
* or it is disabled.
As a consequence, fix usage of testobj_t and mpz_t in the repository

The emulation layer of INIT_MOVE using INIT_SET+CLEAR is removed:
it wasn't working correctly with the local memory context
(INIT_MOVE doesn't need any local memory context to work,
 whereas INIT_SET/CLEAR does)
Remove macro M_DO_INIT_MOVE as it is now useless and uses M_CALL_INIT_MOVE.

The INIT_MOVE default method no longer sets the old 'src' to '0':
it was useless (it doesn't catch any error) and complicates compiler parsing.

Fix POD & A1 & CSTR & classic oplists definition (missing INIT_MOVE operators).

tests/test-mtree.c

@@ -295,31 +295,26 @@ static void test_basic(void)
     tree_move_up(it2, &data);
     tree_get_str(s, t, false);
     assert(string_equal_str_p(s, "[{0,[{-1,[{3}]},{10,[{2,[{1,[{5}]}]}]}]}]"));
-    assert(data == 0);
 
     data = 11;
     tree_move_left(it2, &data);
     tree_get_str(s, t, false);
     assert(string_equal_str_p(s, "[{0,[{-1,[{3}]},{10,[{11},{2,[{1,[{5}]}]}]}]}]"));
-    assert(data == 0);
 
     data = 12;
     tree_move_right(it2, &data);
     tree_get_str(s, t, false);
     assert(string_equal_str_p(s, "[{0,[{-1,[{3}]},{10,[{11},{2,[{1,[{5}]}]},{12}]}]}]"));
-    assert(data == 0);
 
     data = 13;
     tree_move_child(it2, &data);
     tree_get_str(s, t, false);
     assert(string_equal_str_p(s, "[{0,[{-1,[{3}]},{10,[{11},{2,[{13},{1,[{5}]}]},{12}]}]}]"));
-    assert(data == 0);
 
     data = 14;
     tree_move_down(it2, &data);
     tree_get_str(s, t, false);
     assert(string_equal_str_p(s, "[{0,[{-1,[{3}]},{10,[{11},{2,[{14,[{13},{1,[{5}]}]}]},{12}]}]}]"));
-    assert(data == 0);
 
     tree_it_set(&it, root);
     assert(tree_it_equal_p(it, root));