and GNU uses LS_COLORS and GREP_COLORS. So change logic to only set
these environment variables for each OSTYPE.
Also original code was setting the `ls` alias with `-G` instead of
`--color=auto` if in a GNU without `dircolors`. Fix that too.
Simplify arithmetic command expression without using `${var}`, but
`var` instead. The second construct does not fail if `var` is not
defined, but defaults its value to `0` in that case.
Closes#225
6022fe46c5