ftp-client: `ftp-chdir' changes one step at a time.

* guix/ftp-client.scm (%char-set:not-slash): New variable.
  (ftp-chdir): Add docstring.  Change to DIR one step at a time.
  (ftp-retr): Fix indentation.

Merge branch 'core-updates'

Conflicts:
	guix/build/union.scm

ftp-client: Add `ftp-size'.

* guix/ftp-client.scm (ftp-size): New procedure.

Merge branch 'master' into core-updates

Conflicts:
	build-aux/download.scm
	distro/packages/autotools.scm
	distro/packages/base.scm
	distro/packages/bootstrap.scm
	distro/packages/lsh.scm
	distro/packages/make-bootstrap.scm
	distro/packages/ncurses.scm
	distro/packages/perl.scm
	tests/derivations.scm
	tests/union.scm

Update license headers.

Change all license headers, except guix/build/* and ld-wrapper.scm, with
this code:

  (use-modules (guix build utils)
	       (srfi srfi-1))

  (fluid-set! %default-port-encoding "UTF-8")

  (substitute* (remove (lambda (f)
			 (or (string-contains f ".tar.")
			     (string-contains f ".git/")
			     (string-contains f ".so")
			     (string-suffix? ".o" f)
			     (string-suffix? ".a" f)
			     (string-suffix? ".go" f)
			     (string-suffix? ".pdf" f)
			     (string-suffix? ".png" f)
			     (string-suffix? ".info" f)
			     (equal? (basename f) "guix-daemon")
			     (equal? (basename f) "nix-setuid-helper")
			     (string-contains f "nix-upstream/")
			     (string-contains f "distro/packages/bootstrap/")))
		       (find-files "." "\\.[a-z]+$"))
    (("^([[:graph:]]+) This file is part of Guix." _ comment-start)
     (string-append comment-start " This file is part of GNU Guix."))
    (("^([[:graph:]]+) Guix --- Nix package management.*" _ comment-start)
     (string-append comment-start
		    " GNU Guix --- Functional package management for GNU\n"))
    (("^([[:graph:]]+) Guix is " _ comment-start)
     (string-append comment-start " GNU Guix is "))
    (("^([[:graph:]]+) along with Guix." _ comment-start)
     (string-append comment-start " along with GNU Guix."))
    (("^([[:graph:]]+) Copyright \\(C\\)" _ comment-start)
     (string-append comment-start " Copyright ©")))

Change headers using C-style comments manually.

http/ftp: Tweak to avoid depending on libc's NSS.

* guix/build/http.scm (open-connection-for-uri): New procedure.
  (http-fetch): Use it.  Pass the result as a #:port argument to
  `http-get'.
  Add hack to modify the `set-port-encoding!' binding in (web response).

* guix/ftp-client.scm (ftp-open): Add optional `port' parameter,
  defaulting to 21.  When calling `getaddrinfo', convert PORT to a
  string and pass AI_NUMERICSERV when PORT is a number.

ftp-client: Try all the addresses returned by `getaddrinfo'.

* guix/ftp-client.scm (ftp-open): Upon connection failure, try the other
  addresses returned by `getaddrinfo'.

Add (guix ftp) and companion modules.

* 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'.