download: Keep only one slash when concatenating URIs.

* guix/build/download.scm (url-fetch)[uri-vicinity]: New procedure.
  [maybe-expand-mirrors]: Use it.

download: Add support for mirror:// URLs.

* guix/download.scm (%mirrors): New variable.  Mirror lists taken from
  Nixpkgs.
  (url-fetch): New `mirrors' keyword parameter.
  [builder]: Pass it.

* guix/build/download.scm (url-fetch): New `mirrors' keyword parameter.
  [maybe-expand-mirrors]: New procedure.
  [uri]: Use it.

download: Follow HTTP redirections.

* guix/build/download.scm (http-fetch): Follow the redirection when CODE
  is 302.

Remove (guix http) and (guix ftp).

* guix/ftp.scm, guix/http.scm, guix/build/ftp.scm, guix/build/http.scm:
  Remove.
* Makefile.am (MODULES): Likewise.
* tests/builders.scm, distro/packages/base.scm,
  distro/packages/bash.scm, distro/packages/bdw-gc.scm,
  distro/packages/compression.scm, distro/packages/gawk.scm,
  distro/packages/gnupg.scm, distro/packages/gperf.scm,
  distro/packages/guile.scm, distro/packages/libffi.scm,
  distro/packages/libsigsegv.scm, distro/packages/libtool.scm,
  distro/packages/libunistring.scm, distro/packages/lout.scm,
  distro/packages/m4.scm, distro/packages/multiprecision.scm,
  distro/packages/ncurses.scm, distro/packages/perl.scm,
  distro/packages/pkg-config.scm, distro/packages/pth.scm,
  distro/packages/readline.scm, distro/packages/recutils.scm: Use
  `url-fetch' instead of `http-fetch' and `ftp-fetch'.
* distro/packages/bootstrap.scm: Likewise
  (bootstrap-origin): Remove references to `http-fetch' and
  `ftp-fetch'.
* guix.scm (%public-modules): Remove `http' and `ftp'; add `download'.

Add (guix download) and (guix build download).

* guix/download.scm, guix/build/download.scm: New files.
* Makefile.am (MODULES): Add them.
* tests/builders.scm ("url-fetch"): New test.
* distro/packages/bootstrap.scm (bootstrap-origin): Support
  `url-fetch'.
* guix/snix.scm (snix-derivation->guix-package): Use `url-fetch' instead
  of `http-fetch'.

http: Add informative output.

* guix/build/http.scm (http-fetch): Emit message indicating the
  download.

http: Check the HTTP response code, and bail if not 200.

* guix/build/http.scm (http-fetch): Check RESP's code; error out when
  it's not 200.

Add (guix build union).

* guix/build/union.scm, tests/union.scm: New files.
* Makefile.am (MODULES): Add `guix/build/union.scm'.
  (TESTS): Add `tests/union.scm'.

utils: Remove special `substitute*' syntax for lists of files.

* guix/build/utils.scm (substitute*): Remove special syntax for
  list-of-files; instead, check whether FILE is `list?' at run time.

* distro/packages/base.scm (gcc-4.7, %binutils-static): Adjust
  accordingly.

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.

utils: Add `find-files'.

* guix/build/utils.scm (find-files): New procedure.

utils: Add `copy-recursively'; use it.

* guix/build/utils.scm (copy-recursively): New procedure.

* distro/packages/base.scm (%guile-static-stripped): Use it.

utils: Add `mkdir-p'; use it.

* guix/build/utils.scm (mkdir-p): New procedure.

* distro/packages/base.scm (gnu-make-boot0, gcc-boot0-wrapped,
  ld-wrapper-boot3, %static-binaries, %guile-static-stripped): Use it.
* distro/packages/typesetting.scm (lout): Likewise.

utils: Add `fold-port-matches' and `remove-store-references'.

* guix/build/utils.scm (fold-port-matches, remove-store-references): New
  procedures.

* tests/build-utils.scm ("fold-port-matches", "fold-port-matches,
  trickier", "fold-port-matches, with unmatched chars"): New tests.

utils: Add `with-atomic-file-replacement'.

* guix/build/utils.scm (with-atomic-file-replacement): New procedure.
  (substitute): Use it.

Support build-cores = 0; change `guix-build' to default to 0.

* guix/build/gnu-build-system.scm (%parallel-job-count): New variable.
  (build, check): Use it instead of $NIX_BUILD_CORES.

* guix-build.in (guix-build): Default to 0 for the #:build-cores option.

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'.

build-system/gnu: Fix `#:path-exclusions' handling.

* guix/build/gnu-build-system.scm (set-paths)[relevant-input-directories]:
  New procedure.  Use it.  This fixes #:path-exclusions handling.

utils: Make `set-path-environment-variable' verbose.

* guix/build/utils.scm (set-path-environment-variable): Print ENV-VAR
  and its value.

build-system/gnu: Really apply patches.

* guix/build/gnu-build-system.scm (patch): Use `--input FILE', not just
  `FILE'.