readlink/readlink03.c: cleanup

Delete some useless comments.
Use some SAFE_* macros.
Move the test body from main() to readlink_verify().

Signed-off-by: Xing Gu <gux.fnst@cn.fujitsu.com>
readlink/readlink03.c: add ENOTDIR and ELOOP error value tests

add ENOTDIR and ELOOP error value tests for readlink(2)

Signed-off-by: Xing Gu <gux.fnst@cn.fujitsu.com>