Add the --selinux option to be safe with SELinux context restoration

During a test on Fedora 19 I face some issues with SELinux and especially tar.

Example (take a look at the output of ls -Z) :
With tar 1.23 (on RHEL 6.4) : 
```bash
touch /tmp/foo && mv /tmp/foo ~/
ls -Z foo
-rw-r--r--. root root unconfined_u:object_r:user_tmp_t:s0 foo 
tar cf foo.tar foo --xattrs
tar xf foo.tar --xattrs
ls -Z foo
-rw-r--r--. root root unconfined_u:object_r:user_tmp_t:s0 foo 
```

With tar 1.26 (on Fedora 19) :
```bash
touch /tmp/foo && mv /tmp/foo ~/
ls -Z foo
-rw-r--r--. root root unconfined_u:object_r:user_tmp_t:s0 foo
tar cf foo.tar foo --xattrs
tar xf foo.tar --xattrs
ls -Z foo
-rw-r--r--. root root unconfined_u:object_r:admin_home_t:s0 foo
```

This commit add the --selinux option when SELinux is not disabled
What do you think about this weird behaviour ?