Support to define different OS rules in different files.

 - First file that is parsed that defines an OS resolution wins.
 - All versions of an OS must be defined in the same file (for now)
Remove unused imports.
add function to check if view is empty
0.10.8
Add test to reproduce issue 30.
Fix the issue30 test to allow debugging.
Handle catkin package deps (issue 30).
Merge branch 'master' of https://github.com/ros/rosdep
Update test for new version of catkin.
Add attribution.
0.10.9
Add dep on python-catkin-pkg.
Releasing version 0.10.10
Fixed a bug in the makefile
Disabling test for issue #30 until it is fixed.

See issue #37.
Fixed failing test that occurs when not on debian
Added the .travis.yml file to enable CI
Removing unused scripts and modules.

Removed out of date rosdep-gbp-brew and related
rosdep2.platforms.brewmaker module, because
it is out of date.
Merge pull request #36 from ros/remove_unused_scripts

Removing unused scripts and modules.
Added catkin_packages module.

This new module contains code for finding catkin
packages in arbitrary folders and storing the
results.