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-obj-except.h

@@ -236,6 +236,7 @@ static inline size_t test_obj_except__hash(const test_obj_except__t z)
    INIT_SET(test_obj_except__init_set),                                          \
    SET(test_obj_except__set),                                                    \
    CLEAR(test_obj_except__clear),                                                \
+   INIT_MOVE(M_COPY_A1_DEFAULT),                                      \
    TYPE(test_obj_except__t),                                                     \
    ADD(test_obj_except__add),                                                    \
    OUT_STR(test_obj_except__out_str),                                            \