tests: make echo tests robust to build directory
The behaviour of echo command is to print exactly as the arguments are,
unless -n is in which the escape chars are recognized.
Make test scripts POSIX compliant
"." with argument is not POSIX compliant, so it must be removed.
Instead, set tool directly in the test scripts.
test/chmod: fix awk usage
test/unlink: use hardlink instead of symlink
cmp: fix -s, add man page
unlink: move to XSI group
test/chmod: make executable
chmod: add conformance test
unlink: add conformance test