JsonObject: bugfix to getStringProperty with non-null terminated C string
JsonObject: minor fixes to deserialize

ensure that param_count >= 0
style fix
unit test: fix incorrect use of boost::shared_ptr

DIET_client_mock_unit_tests/my_test_serial_n
boost::shared_ptr::get allows to retrive a raw pointer but nothing
guarantees that it will remain usable during the whole scope of your test
You should retrieve the smart pointer and then use get when you need to pass
a raw pointer to *legacy* methods.