Implement multiarch support in catkin

commit e99145af8fb2d46022395806e34d9468a4e0df92
Author: Steven Peters <scpeters@osrfoundation.org>
Date:   Mon May 5 16:45:19 2014 -0700

    Updates per comments by @dirk-thomas

    Remove shell keyword and call Popen with list of strings.
    Remove extra : from PATH variable packing.
    Fix indentation.
    Use " to fix escaped single quotes.

commit a0eb2a0ac790f39d8e99f32c45f094479f0102c2
Author: Steven Peters <scpeters@osrfoundation.org>
Date:   Mon May 5 15:11:28 2014 -0700

    Don't check multiarch on non-Linux systems

commit 655012a59b06825732ec6a31594f69b8670a4084
Author: Steven Peters <scpeters@osrfoundation.org>
Date:   Mon May 5 14:45:47 2014 -0700

    Updates per comments from @wjwwood

    Renamed the CATKIN_MULTIARCH_*_DESTINATION variables to
    CATKIN_*_ENVIRONMENT_PATHS.
    Use isinstance to verify that variables are lists.
    Check Popen return code instead of std_err.
    Fix logic error in catkin_generate_environment.cmake