master is broken due to latest changes to pk-mi-json

[Jose E. Marchesi]

Hi kostas, all.

The master branch is broken for me:

gcc -DHAVE_CONFIG_H -I. -I../../poke  -I../gl -I../../gl -I../../common 
-I../../libpoke -I../libpoke -DJITTER_VERSION=\"0.9.270\" 
-DPKGDATADIR=\"/usr/local/share/poke\" -DPKGINFODIR=\"/usr/local/share/info\" 
-DLOCALEDIR=\"/usr/local/share/locale\"  -Wall -I/usr/include/json-c -g -O2 -MT 
poke-pk-mi-json.o -MD -MP -MF .deps/poke-pk-mi-json.Tpo -c -o poke-pk-mi-json.o 
`test -f 'pk-mi-json.c' || echo '../../poke/'`pk-mi-json.c
../../poke/pk-mi-json.c: In function 'pk_mi_val_to_json_1':
../../poke/pk-mi-json.c:161:15: error: void value not ignored as it ought to be
     int ret = json_object_object_add (obj, key, val);                         \
               ^

My version of libjson-c has a json_object_object_add that doesn't return
any value:

extern void json_object_object_add(struct json_object* obj, const char *key,
                                   struct json_object *val);

I would suggest to fix it by creating a wrapper function like:

static inline int
pk_json_object_object_add (struct json_object* obj, const char *key,
                           struct json_object *val)
{
#if HAVE_JSON_OBJECT_OBJECT_ADD_RETURN_VALUE
  return json_object_object_add (obj, key, val);
#else
  json_object_object_add (obj, key, val);
  return WHATEVER_OK;
#endif
}

The HAVE_JSON_OBJECT_OBJECT_ADD_RETURN_VALUE should be set at configure
time.

Could you please take a look to this?
Thanks.