Unbreak test tools, allowing building with gcc-14 The test-send-xmessage* tools were passing pointers (to argv) to interfaces that expect ints (32 bit IDs). This looks like it has never worked, but I don't know why nobody noticed earlier.
Also document that, because the message type parameters are strings in sn_internal_add_xmessage_func and numeric IDs in sn_internal_broadcast_xmessage, this is also the case in the testing tools.
Debian already does not run or ship these testing tools, but it does build them, which fails in GCC 14.
