expose PYTHON_EXECUTABLE to environment hook .em templates
ignore cd path echo when using CDPATH, which breaks catkin usage

see http://superuser.com/questions/90535/how-do-i-turn-of-auto-echo-in-bash-when-i-cd
reset CATKIN_SHELL in devel space generated env.sh files (fix #652)
reset CATKIN_SHELL in devel space generated env.sh files, second location (#655)
update changelog
0.5.88