Rosinstall

------

- minor bugfix for 41, setupfiles not regenerated causing rosbash missing on pre-fuerte
- changes to docstrings and some messages

------

- minor bugfixes for 34, 35

------

- fixed 33 sed -s blunder

------

- bugfix rosinstall --snapshot not working (refactoring victim)
- minor bugfixes on options of rosws update
- pyyaml added as dependency in setup.py, rather than failure on import

------

- undoing bash completion install as it fails with easy_install

-----

- fix 25 rejection of git short-hand notation userserver:file
- Create a .rosinstall.bak on every rewrite
- diverse minor bugs
- strictly accept only one ros root in workspace
- parallelity is non-default for init and update, options -j and --parallel like cmake
- setup.sh also infers ROS_ROOT from .rosinstall
- docs contain tutorial for rosws
- more verbose out of paralelity
- added this changelog
- more versatile info command --only option
- bugfix unable to add plain folder
- allow to set version to None