update tutorials to depend on message_generation instead of genmsg

[dirk-thomas]

[jack-oquin]

This affect several ROS wiki tutorials as well as this package.

• http://answers.ros.org/question/65236/what-is-difference-between-message_generation-and-genmsg/
• see also: issue #6

[jack-oquin]

dirk-thomas: you can assign this and #6 to me, if you like.

[JanSurft]

There is a dependency on genmsg in the publisher/subscriber tutorial here: http://wiki.ros.org/ROS/Tutorials/WritingPublisherSubscriber%28c%2B%2B%29.

It begins at 3. Building your nodes

[LukeAI]

this is still the case^

[LukeAI]

this is still the case^