(process_init_element): Special handling for {"foo"}.
(struct constructor_stack): New field `replacement_value'.
(push_init_level, really_start_incremental_init): Clear new field.
(pop_init_level): Return the replacement_value if any.
At top level in initializer, output that value,
and set the array size from it.

(digest_init): Delete arg TAIL.  Fix all calls.

(convert_for_assignment): Mismatch in signedness
of pointer targets should not inhibit warnings for const mismatch.

From-SVN: r5042