include/safe_macros.h: fix mistakes

* safe_fstat --> safe_stat
* safe_fstat --> safe_lstat

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>
fchownat/fchownat01.c: cleanup

* Delete some useless commtents.
* Create fchownat.h to encapsulate fchownat(2)
* Use SAFE_* macros.
* Some cleanup.

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>
fchownat/fchownat02.c: add a new test

Add AT_SYMLINK_NOFOLLOW test for fchownat(2)

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>