amcl: wrap tests in CATKIN_ENABLE_TESTING check
costmap_2d: fixup tests

This includes using the catkin_add_gtest macro,
using catkin_download_test_data, configuring tests
only if CATKIN_ENABLE_TESTING is set, and ensuring
rostests looked in the correction location for
files which were downloaded.
costmap_2d: changed a function to take a pointer

This fixes a warning from clang:

```
/Users/william/nav_ws/nav_only_ws/src/navigation/costmap_2d/src/costmap_2d_publisher.cpp:48:11: warning: initializing pointer member 'node' with the stack address of parameter
      'ros_node' [-Wdangling-field]
    node(&ros_node), costmap_(costmap), global_frame_(global_frame), active_(false), always_send_full_costmap_(always_send_full_costmap)
          ^~~~~~~~
/Users/william/nav_ws/nav_only_ws/src/navigation/costmap_2d/include/costmap_2d/costmap_2d_publisher.h:95:20: note: pointer member declared here
  ros::NodeHandle* node;
                   ^
1 warning generated.
```
navfn: add missing dependency on netpbm for tests
navfn: netpbm is include namespaced on OS X