Add comparison of object`s size in JValue::operator==

One more api was added to perform object`s size calculation.

[GF-6379]libpbnjson: JValue::operator==(JValue) does not check objects' size

Open-webOS-DCO-1.0-Signed-off-by: Alekseyev Oleksandr <oalekseyev@luxoft.com>

Change-Id: I7100405fcad9ec9042dd98fe25cd0557e1f47ac0
Add one more overload for JValue::operator==

JValue::operator==(const char *) was added in order to prevent C++ resolve const char * to bool.

[GF-6378]libpbnjson: JValue tries to compare C strings as booleans

Open-webOS-DCO-1.0-Signed-off-by: Alekseyev Oleksandr <oalekseyev@luxoft.com>

Change-Id: I6dc9013f31b4d011d3a3b39acc32e3a41ffdb509