* guix/ftp-client.scm (ftp-open): Upon connection failure, try the other addresses returned by `getaddrinfo'.
* guix/ftp-client.scm, guix/ftp.scm, guix/build/ftp.scm: New files. * Makefile.am (MODULES): Add them. * distro/base.scm (libffi): Use `ftp-fetch'.