Autoproj v2.1.0

Improvements:

• improved the feedback on env.sh updates. The message is different if env.sh was modified (updated: …) vs. left the same (left unchanged: …)
• re-added the -n shortcut for --no-deps
• the tag and commit subcommands add dependencies by default
• added a progress spinner when status stops for long (more than 1s)
• added --help to aup and amake
• automatically update bundler itself
• added osdeps --system-info to find out how the local OS is detected by autoproj

Bugfixes:

• an empty overrides: entry in autoproj/overrides.yml is properly handled
  (fixes #137)
• resolve configuration variables in VCS information the way v1 was (fixes #135)
• fix autoproj clean (fixes #139)
• update env.sh after a build (fixes https://github.com/doudou/rock_website/issues/1)
• add PIP_HOME/bin to PATH in the pip osdep handler
• do update an invalid package set (a package set without a name) even if -k
  was not given
• in status, on packages pinned by a commit or tag, do not show commits in advance of this tag/commit.