Some updates for GenerateRTTROSCommPackage.cmake.em

* The `rtt_roscomm_destinations()` macro has been called before `find_package(OROCOS-RTT ...)`. The `ORO_USE_*` variables might not have been set yet, if Orocos has not been found previously. This is the case when a package created with `create_rtt_pkg` is compiled in a catkin workspace without other packages or for rosbuild.
  I also moved the set command of related cmake variables out of the loop as they are independent of the message name.
* The `ADDITIONAL_MAKE_CLEAN_FILES` property was overridden if typekit and service proxy macro have been called within the same directory.
* The `ADDITIONAL_MAKE_CLEAN_FILES` list contained only the catkin-specific include folder in `ros_generate_rtt_typekit()`.

I tested this patch manually with
* catkin_make_isolated build with all packages in rtt_ros_integration, rtt_ros_comm and rtt_common_msgs.
* building catkin typekit packages in a workspace overlaying the rtt_ros_integration install-space.
* building rosbuild typekit packages for catkin and rosbuild message packages.