Add M_INIT_VAI to initialize a container with a VA.

(pretty much like it was done for ALGO).
Use if for array & list so that you can init them in M_LET
by giving it a VA.

m-list.h

@@ -56,6 +56,7 @@
 #define LISTI_OPLIST2(name, oplist)                                     \
   (INIT(M_C(name, _init)),						\
    INIT_SET(M_C(name, _init_set)),					\
+   INIT_WITH(API_1(M_INIT_VAI)),                                        \
    SET(M_C(name, _set)),						\
    CLEAR(M_C(name, _clear)),						\
    MOVE(M_C(name, _move)),						\