add error message for circular dependencies in catkin_make_isolated and catkin_topological_order (fix #607, fix #608)
remove underlay doc which is completely covered in the ROS wiki
fix gtest include dir when using gtest inside the workspace (fix #585)
clarify gtest that a checkout inside the workspace only works for a workspace build not in isolation
use underlay workspaces when calculating topological order
remove invalid symbolic links of workspace level CMakeLists.txt file (fix #591)
support setting _LIBRARIES before invoking catkin_package()
Do not call chpwd hooks in setup.zsh

By default, cd'ing on zsh calls the shell function chpwd. This is commonly used for things like showing the current directory in the title terminal by printing a string with some escape codes, but this breaks _CATKIN_SETUP_DIR. `-q` disables the chpwd hooks.

The zshbuiltins(1) man page writes about -q: "If  the -q (quiet) option is specified, the hook function chpwd and the functions in the array chpwd_functions are not called. This is useful for calls to cd that do not change the environment seen by an interactive user."
fix bad usage of IMPORTED_IMPLIB by IMPORTED_LOCATION
consider test_depends for dependencies
python: fix python path setting in plain cmake workspaces

In plain cmake workspaces the python install dir is set to
lib/python2/dist-packages instead of lib/python2.7/dist-packages

I checked the catkin/cmake/python.cmake file and in that file there is
an extra check for the version, so I assume that we should only use
the major version in case the major version is 3 or higher.
fix catkin_find to not return path with '/.' suffix
set catkin_* variables only when find_package(catkin COMPONENTS ...)
allow better performance for repeated invocations of find_in_workspaces()
fix problem when cm / cmi is invoked in a symlinked folder using e.g. --directory (fix #638)
fix rollback of environment when workspace has been deleted
add unit test to check that cmi invocation on an empty workspace does not fail
add unit test to check that cmi invocation from symlinked subfolders does not fail
fix ansi unit test
fix argument handling when cm / cmi is invoked in a symlinked folder (#638)