First draft of sensor interfaces.

- Force/torque (wrench)
- Orientation
- IMU (very crude approximation)
Add sensor reference frame field.
Add sensor ref frame field and capability queries.
Merge branch 'master' into sensor_interfaces
Scrape orientation interface prototype.
Explicitly initialize IMU sensor handle members.
Remove Eigen dependency from hardware_interface.

- Expose force-torque and IMU sensor data as const pointers to the raw data.

- Client code should wrap raw data however they prefer.
Merge branch 'master' into sensor_interfaces
Merge branch 'master' into sensor_interfaces
Merge branch 'master' into sensor_interfaces
Update sensor interfaces implementation.

- Use resource managing classes introduced in recent hardware interface rework.

- Conform to unified public API.
Merge branch 'master' into sensor_interfaces
Add missing brace.
Merge branch 'master' into sensor_interfaces
Merge branch 'master' of github.com:willowgarage/ros_control
User error checking
Merge branch 'master' of github.com:willowgarage/ros_control
Merge branch 'fuerte_backport' into sensor_interfaces
Merge pull request #70 from pal-robotics/master

Make specific transmission interfaces proper types.
Merge pull request #67 from davetcoleman/master

Added user error checking to namespace argument