Terminal: Disable color output when CLICOLOR is set to 0
These commits complete the color output control support. Previously, color output could only be forced ON by setting the environment variable CLICOLOR_FORCE to 1. With this commit, color output can also be disabled, by setting the environment variable CLICOLOR to 0. This can be useful e.g. for processing of build logs when the cmake run happens within a container (where isatty is true), but the processing happens on the outside.
See http://bixense.com/clicolors/ for documentation of this convention.
Topic-rename: Terminal-clicolor
Edited by Brad King