build: Add and export procedure 'register-root*'.

* guix/scripts/build.scm (register-root*): Add and export it.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

environment: Deal with single-entry search paths.

This is a followup to fcd75bdbfa99d14363b905afbf914eec20e69df8.

* guix/scripts/environment.scm (create-environment): Check whether
SEPARATOR is #f.

doc: Add "Documentation" section.

* doc/guix.texi (Documentation): New node.

profiles: Generate database file for man pages.

The mandb database file (index.db) is used by the "apropos" (whatis) or
"man -k" commands.  This change introduces a profile hook to generate
such database file.

* guix/profiles.scm (manual-database): New procedure.
(%default-profile-hooks): Add it.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>

build-system/python: 'package-with-explicit-python' uses 'package-mapping'.

* guix/build-system/python.scm (package-with-explicit-python)
[package-variant, cut?]: New procedures.
[transform]: Remove 'mlambdaq' form and input tuple handling.
Use 'package-mapping'.

packages: Add 'package-mapping' and base 'package-input-rewriting' on it.

* guix/packages.scm (package-mapping): New procedure.
(package-input-rewriting): Rewrite in terms of 'package-mapping'.
* tests/packages.scm ("package-mapping"): New test.
* doc/guix.texi (Defining Packages): Document it.

Revert "gnu: openexr: Add IlmBase include sub-directory to 'OpenEXR.pc'."

This reverts commit 01fe019166fe8a925b3bf3b489792b52b1b6ca7a,
which was unneeded because IlmBase is already listed as 'Requires'
in 'OpenEXR.pc'.

Revert "gnu: bc: Update to 1.07."

This reverts commit dfee7daedb760f1b1d7506829ca31633f4173356.  It causes
the linux-libre@4.9 build to hang (command-line usage works fine).

gnu: Move audacity to audio.scm.

* gnu/packages/audacity.scm: Remove file and move audacity...
* gnu/packages/audio.scm: ...here.
* gnu/local.mk: Remove reference to removed file.

import cran: Distinguish Bioconductor data packages.

* guix/import/cran.scm (bioconductor-package?): Exclude Bioconductor
data packages.
(bioconductor-data-package?): New procedure.

gnu: sra-tools: Fix glibc naming conflict.

* gnu/packages/bioinformatics.scm (sra-tools)[arguments]: Add build phase
"patch-away-glibc-conflict" to fix a definition conflict with glibc 2.25.

gnu: sra-tools: Use "modify-phases" syntax.

* gnu/packages/bioinformatics.scm (sra-tools)[arguments]: Use "modify-phases"
syntax.

gnu: diamond: Update to 0.8.37.

* gnu/packages/bioinformatics.scm (diamond): Update to 0.8.37.

download: Update the GnuPG mirror list.

* guix/download.scm (%mirrors) <gnupg>: Use HTTP for TU Wien mirror.

gnu: kdevelop: Update to 5.1.0.

* gnu/packages/kde.scm (kdevelop, kdevplatform): Update to 5.1.0.

gnu: bc: Update to 1.07.

* gnu/packages/algebra.scm (bc): Update to 1.07.
[native-inputs]: Add ed and texinfo.
[arguments]: Use default ‘configure’ phase.

gnu: bc: Actually use readline.

* gnu/packages/algebra.scm (bc)[arguments]: Add ‘--with-readline’
to #:configure-flags.

gnu: algebra: Re-order imports.

* gnu/packages/algebra.scm: Order imports alphabetically.

gnu: openexr: Add IlmBase include sub-directory to 'OpenEXR.pc'.

* gnu/packages/graphics.scm (openexr)[arguments]: Add
'set-ilmbase-directory-in-pc-file' phase.

services: cuirass: Wait for networking.

* gnu/services/cuirass.scm (cuirass-shepherd-service): Add 'networking'
to 'requirements'.