packages: Accept <origin> as package inputs.

* guix/packages.scm (package-derivation): Accept use of an <origin> as
  an input.

packages: Add `package-full-name'.

* guix/packages.scm (package-full-name): New procedure.
  (package-derivation): Use it.

Move <location> to (guix utils).

* guix/packages.scm (<location>, location): Move to...
* guix/utils.scm: ... here.

packages: Add `package-transitive-propagated-inputs'.

* guix/packages.scm (transitive-inputs): New procedure.
  (package-transitive-inputs): Rewrite in terms of `transitive-inputs'.
  (package-transitive-propagated-inputs): New procedure.

packages: Cache the result of `package-derivation'.

* guix/packages.scm (%derivation-cache): New variable.
  (cache, cached-derivation): New procedures.
  (package-derivation): Use them.

packages: Add a printer for <package>.

* guix/packages.scm (<package>): Add record printer.

packages: Raise an error condition upon invalid input.

* guix/packages.scm (&package-error, &package-input-error): New
  condition types.
  (package-derivation): Raise a `&package-input-error' when no match is
  made.

packages: Add all non-derivation paths to the store.

* guix/packages.scm (package-derivation): Add all non-derivation paths
  to the store.

packages: Allow store paths as inputs.

* guix/packages.scm (package-derivation): Allow non-derivation store
  paths as inputs.

Add `package-transitive-inputs'; use it to honor propagated inputs.

* guix/packages.scm (package-transitive-inputs): New procedure.
  (package-derivation): Use it to compute INPUTS.

* tests/packages.scm (dummy-package): New macro.
  ("package-transitive-inputs"): New test.

packages: Allow inputs that are local files.

* guix/packages.scm (package-derivation): Add to the store inputs that
  are local files.

packages: Add a `self-native-input?' field.

* guix/packages.scm (<package>)[self-native-input?]: New field.
  (package-derivation): Update/fix pattern.

Rename <package-source> to <origin>; use the `letrec*' behavior in packages.

* guix/packages.scm (<package-source>): Rename to...
  (<origin>): ... this.  Update users.

* distro/base.scm (libsigsegv, gawk, hello): Adjust to renaming; refer
  to VERSION to build the URL.

Add a `base32' macro, for convenience.

* guix/packages.scm (base32): New macro.

* distro/base.scm (libsigsegv, gawk, hello): Use it.

packages: Allow the `arguments' field to be a procedure.

* guix/packages.scm (package-derivation): When ARGS is a procedure, call
  (ARGS SYSTEM).

* distro/base.scm (gawk)[arguments]: Turn into a procedure, to disable
  tests on Cygwin.

Add `propagated-inputs' and `properties' to <package>.

* guix/packages.scm (<package>)[propagated-inputs, properties]: New
  fields.
  (package-derivation): Update `match' clause.

distro: Add libsigsegv and GNU Awk.

* guix/packages.scm (<package>)[arguments]: Default to '().

* distro/base.scm (libsigsegv, gawk): New packages.
  (hello): Use GAWK instead of (nixpkgs-derivation "gawk").

packages: Add a `home-page' field.

* guix/packages.scm (<package>)[home-page]: New field.

* distro/base.scm (hello)[home-page]: Initialize.

Track the source location of packages.

* guix/packages.scm (<location>): New record type.
  (location, source-properties->location): New procedures.
  (<package>)[location]: New field.

* tests/packages.scm ("GNU Hello"): Test `package-location'.

Add a declarative packaging layer.

* Makefile.am (MODULES): Add `guix/packages.scm' and `distro/base.scm'.
  (TESTS): Add `tests/packages.scm'.
  (EXTRA_DIST): New variable.

* guix/packages.scm, distro/base.scm, tests/packages.scm: New files.

* guix/http.scm (http-fetch): Make `name' an optional argument, to match
  the expectations of `package-source-derivation'.