Add missing libarchive flags, some security tests

[ghost]

Hi,

I've been using your library to process untrusted archives provided by the users and have noticed that two flags were missing, one of which is important when dealing with untrusted input (EXTRACT_SECURE_NOABSOLUTEPATHS).

They have been supported by libarchive for around two years so it's a stable feature that I think should be merged to your library. Take a look at man archive_write_disk.3 for details.

This pull request adds them and provides a couple of tests for two security features that are important to me at the moment.
I'll add more tests to cover the remaining flags when I have some free time.

Thanks for a great library, it saved me a lot of work.

Cheers.

--

• Add missing flags supported by libarchive:

  • EXTRACT_SECURE_NOABSOLUTEPATHS;
  • EXTRACT_CLEAR_NOCHANGE_FFLAGS;

• Add some tests for security options:

  • EXTRACT_SECURE_NODOTDOT;
  • EXTRACT_SECURE_NOABSOLUTEPATHS.

[ghost]

Hmm, it seems that one of the flags was added in libarchive v.3.1.900, while Travis CI build uses 3.1.2, which was released two years before that. I'll try to work around it by checking which version of the library we are using, if at all possible.

[Changaco]

Looks okay to me.