guix package: Add '--do-not-upgrade' option.

* guix/scripts/package.scm (%options): Add the '--do-not-upgrade' option.
  (show-help): Document it.
  (options->installable): Add 'do-not-upgrade-regexps' variable.
  Use it in 'packages-to-upgrade'.
* doc/guix.texi (Invoking guix package): Document the '--do-not-upgrade'
  option.

doc: Add example showing how to customize 'nscd-service'.

* doc/guix.texi (Name Service Switch): Add link to nss-mdns.  Add
  example show how to pass #:name-services to 'nscd-service'.
  (Base Services): Add link from 'nscd-service' to the above.
* gnu/services/base.scm (nscd-service): Update docstring accordingly.

activation: Remove undeclared user accounts and groups.

Fixes <http://bugs.gnu.org/19795>.
Reported by David Thompson <dthompson2@worcester.edu>.

* gnu/build/activation.scm (enumerate, current-users, current-groups,
  delete-user, delete-group): New procedures.
  (activate-users+groups): Add calls to 'delete-user' and
  'delete-group'.
* doc/guix.texi (User Accounts): Add a paragraph about statelessness.
  Explain that passwords are preserved.

import: Add hackage importer.

* guix/scripts/import.scm (importers): Add hackage.
* guix/scripts/import/hackage.scm: New file.
* po/guix/POTFILES.in: Add guix/scripts/import.scm.
* doc/guix.texi: Add section on 'hackage' importer.

doc: Refer to "Substitutes" from "Setting Up the Daemon".

Suggested by Mark H Weaver.

* doc/guix.texi (Setting Up the Daemon): Add xref to "Substitutes".

doc: Mention the relation between module names and file names.

* doc/guix.texi (Package Modules): Mention the relation between module
  names and file names.

doc: Mention that the current generation is not deleted.

* doc/guix.texi (Invoking guix package): Mention that the current
  generation is not deleted.  This is a followup to d26eb84.

scripts: Add 'publish' command.

* guix/scripts/publish.scm: New file.
* po/guix/POTFILES.in: Add it.
* tests/publish.scm: New file.
* Makefile.am (MODULES): Add script module.
  (SCM_TESTS): Add test module.
* doc/guix.texi ("Invoking guix publish"): New node.

build-system: Add haskell-build-system.

* guix/build-system/haskell.scm: New file.
* guix/build/haskell-build-system.scm: New file.
* doc/guix.texi: Add section on 'haskell-build-system'.

services: lsh: Change #:initialize? to default to #t.

* gnu/services/ssh.scm (lsh-service): Change #:initialize? to default
  to #t.
* doc/guix.texi (Using the Configuration System): Remove #:initialize? #t
  from example.
  (Networking Services): Adjust accordingly.

doc: Make it clear that store items must not be deleted by hand.

* doc/guix.texi (Invoking guix gc): Add that this is the only way to
  delete files.

doc: Remove bits about having to create /gnu/store manually.

* doc/guix.texi (Build Environment Setup): Remove bit about creating
  /gnu/store.  This is done automatically since 15ddeff.

services: syslog-service: Add 'config-file' argument.

* gnu/services/base.scm (syslog-service): Add 'config-file' keyword
argument.
* doc/guix.texi (Base Services): Document it.

gexp: Add 'local-file'.

* guix/gexp.scm (<local-file>): New record type.
  (local-file): New procedure.
  (local-file-compiler): New compiler.
  (gexp->sexp) <struct? thing>: Handle the case where 'lower' returns a
  file name.
  (text-file*): Update docstring.local-file doc
* tests/gexp.scm ("one local file", "gexp->derivation, local-file"): New
  tests.
* doc/guix.texi (G-Expressions): Mention local files early.  Document
  'local-file'.  Update 'text-file*' documentation.

doc: Update gexp wrt. extensibility.

This is a followup to bcb1328.

* doc/guix.texi (G-Expressions): Move paragraph about extensibility
  below.  Remove assumptions that things are either packages or
  derivations.

services: Add 'lirc-service'.

* gnu/services/lirc.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add it.
* doc/guix.texi (Various Services): New node.  Document 'lirc-service'.

doc: Add section about the test suite.

* doc/guix.texi (Running the Test Suite): New section.

gexp: Move the package and origin compilers to (guix packages).

From now own, (guix packages) depends on (guix gexps); it was the other
way around now.  This means that (guix packages) code can use gexps.

* guix/gexp.scm (origin-compiler, package-compiler): Remove.
  (default-guile-derivation): New procedure.
  (gexp->derivation): Use it instead of 'default-guile' +
  'package->derivation'.
* guix/packages.scm (default-guile-derivation): New procedure.
  (package-compiler, origin-compiler): New variables.
* doc/guix.texi (G-Expressions): Mention extensibility.

services: slim: Use /run/current-system/profile/share/xsessions as sessiondir.

* gnu/services/xorg.scm (<session-type>, %windowmaker-session-type)
  (%ratposion-session-type, %sawfish-session-type, %default-xsessions)
  (xsessions-directory): Remove.
  (slim-service): Remove #:sessions parameter.
  [slim.cfg]: Use /run/current-system/profile/share/xsessions as sessiondir.
* doc/guix.texi <X Window>: Adjust accordingly.

doc: Suggest to use 'lsh-service' with #:initialize? #t.

Suggested by Tomáš Čech.

* doc/guix.texi (Using the Configuration System): Pass #:initialize? #t
  to 'lsh-service'.