Refactor: do not check whether '.' exists, and no possibly unused call to abspath
part of #304 create a workspace marker file when build succeeded.
documentation: less ambiguous docstring
part of #304: python function in catkin/workspace.py to retrieve parent workspace
Refactor: Renamed var and value, extracted+reused ensure function. fix typos
part of #304: run catkin_make in ancestor containing marker file, if any
part of #304: unit tests
(part of #304) shell script exposing python function to get workspace root
better arg validation:
- argparse validation of passed path argument
- return -1 instead or errno error code
- argparse --help prints default value for path