[API] Fixed copy constructing from a void client.

Do not connect session signals if the session pointer isn't initialized
in the first place. That might happen when copy initializing a new
client.
[Locator] Fixed BH stealing UUIDs.

BH's scoped_attributes_t attribute::make helper function was stealing
remote_client_t's UUID class data field, because for some weird reason,
the T&& overload was being called instead of a const T& one. Fixed by
marking the UUID class data field const.
[Actor] Make endpoint resolution a little faster.

Tell the resolver that 'service' is actually a port number, so there's
no need to resolve it as well.
[ASIO] Fixed the usage of post()/dispatch().

Use dispatch() only when there's a change for this function to be called
from inside the reactor. Use post() to be 100% sure that the calling
object won't be destroyed while in the call.
Naming!