add script to doctor workspace

a script to check workspace soundness

* check ROS_PACKAGE_PATH is sound
* check git repositories under workspace are sound

* the result of my environment
![2014-06-13 17 08 52](https://cloud.githubusercontent.com/assets/40454/3267799/9e799570-f2d2-11e3-9a62-c39540ab24ea.png)

* applications@pr1040 with `~/.bashrc`
![2014-06-13 17 10 10](https://cloud.githubusercontent.com/assets/40454/3267800/9e79a664-f2d2-11e3-9ee2-8668606c062e.png)
* applications@pr1040 with `ros/hydro/devel/setup.bash`
![2014-06-13 17 14 04](https://cloud.githubusercontent.com/assets/40454/3267807/bbafc484-f2d2-11e3-936e-bc56f90fe220.png)