Improve default env settings and avoid "set -e" in the sourced script

centos6_env.sh: new/better default for centos6
env/finish.sh: remove "set -e" management in favor of ERR traps
env/start.sh: ditto, and remove CORBA default = 1
jkmac_env_darwin_x86_64.sh: remove "set -e" management in favor of ERR traps
jkamd_env_linux_x86_64.sh: ditto