removes dupes from fish variable (taken from fish issue #296)

varclear.fish

function varclear --description 'Remove duplicates from environment variable'
    if test (count $argv) = 1
        set -l newvar
        set -l count 0
        for v in $$argv
            if contains -- $v $newvar
                set count (math $count+1)
            else
                set newvar $newvar $v
            end
        end
        set $argv $newvar
        test $count -gt 0
        and echo Removed $count duplicates from $argv
    else
        for a in $argv
            varclear $a
        end
    end
    return 0
end