more bugfixes for roscore compatibility

[jobafr]

changes:

• return correct error when querying a missing parameter (previously, this would show up as a rospy.core.rosgraph.MasterError in the rospy API)
• when param subscribers return (1, "", 0) instead of (), don't treat that as an error (apparently some clients do this)
• make topic type mismatch a soft error, allow subscribing to * type (fixes rosbag record. upstream roscore allows using different types on the same topic. * is used when a subscriber doesn't care about the exact type, like rosbag. When a subscriber tries to connect to an incompatible publisher, this results in a warning on the client's side when using rospy, and is not handled by roscore. The previous behavior of ros-core-rs would be that the subscriber's API call fails entirely, which is different than what roscore does.)

[PatWie]

Super cool. Thanks for looking into it.