Add attach_options.h to the list of included files

Without this, make dist doesn't include it and LXC fails to build.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Add a local implementation of ifaddrs.h

This adds a local ifaddrs implementation to be used on Bionic or other C
libraries that don't come with a getifaddrs implementation.

This code was written by Kenneth MacKay and is under a two-clause BSD
license (copyright information in the file headers).

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Replace all calls to rindex by strrchr

The two functions are identical but strrchr also works on Bionic.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>