* tests/cp/cp-a-selinux: New file. Test for the bug reported in

* tests/cp/cp-a-selinux: New file. Test for the bug reported in

* tests/cp/Makefile.am (TESTS): Add cp-a-selinux.

* tests/selinux: New file.
* tests/Makefile.am (EXTRA_DIST): Add selinux.
* tests/misc/selinux: Source the new script, rather than open coding it.

Change how "cp -a" and "cp --preserve=context" work with SELinux.
Now, cp -a attempts to preserve context, but failure to do so does
not change cp's exit status.  However "cp --preserve=context" is
similar, but failure *does* cause cp to exit with nonzero status.
* src/copy.h (struct cp_options) [require_preserve_context]: New member.
* src/copy.c (copy_reg, copy_internal): Implement the above.
* src/mv.c (cp_option_init): Initialize the new member.
* src/install.c (cp_option_init): Likewise.
* src/cp.c (cp_option_init): Likewise.
(decode_preserve_arg): Set it or reset it.

FIXME: add an on-writable-NFS-only test