my $base = "ftp:/a/b";
URI->new_abs("/c/d", $base)     -> "ftp:/c/d"
URI->new_abs("e/f/../g", $base) -> "ftp:/a/e/g"
URI->new_abs("../g", $base)     -> "ftp:/g"
URI->new_abs("../../i", $base)  -> "ftp:/../i"
URI->new_abs("../../j/k/l/../m", $base) -> "ftp:/../j/k/m"