The lack of mjson_next() prevents to iterate easily and need to hack by
iterating on a loop of snprintf + $.field[XXX] combined with
mjson_find().
This reintroduce mjson_next() so we could iterate without having to
build the string.
The patch does not reintroduce MJSON_ENABLE_NEXT so it could be used
without having to define it.
This library is required for the subsequent patch which adds
the JSON query possibility.
It is necessary to change the include statement in "src/mjson.c"
because the imported includes in haproxy are in "include/import"
orig: #include "mjson.h"
new: #include <import/mjson.h>
