derivations: Add 'substitution-oracle' and use it.

This makes 'guix environment PACKAGE' significantly faster when
substitutes are enabled.  Before that, it would lead to many invocations
of 'guix substitute-binary', one per 'derivation-prerequisites-to-build'
call.  Now, all these are replaced by a single invocation.

* guix/derivations.scm (derivation-output-paths, substitution-oracle):
  New procedures.
  (derivation-prerequisites-to-build): Replace #:use-substitutes? with
  #:substitutable?.  Remove the local 'derivation-output-paths' and
  'substitutable?'.
* guix/ui.scm (show-what-to-build): Add 'substitutable?'.  Pass it to
  'derivation-prerequisites-to-build'.
  [built-or-substitutable?]: Use it instead of 'has-substitutes?'.
* tests/derivations.scm ("derivation-prerequisites-to-build and
  substitutes"): Use #:substitutable? instead of #:use-substitutes?.

derivations: Add 'derivation-output-names'.

* guix/derivations.scm (derivation-output-names): New procedure.
  (derivation-prerequisites-to-build): Use it for #:outputs.
  (map-derivation): Likewise.
* tests/derivations.scm ("derivation-output-names"): New test.

nls: Update 'eo' translation.

import: Add CPAN importer.

* guix/import/cpan.scm, guix/scripts/import/cpan.scm, tests/cpan.scm:
  New files.
* Makefile.am (MODULE)[HAVE_GUILE_JSON]: Add them.
* guix/scripts/import.scm (importers): Add cpan.
* doc/guix.texi (Requirements): Mention `guix import cpan` as a user
  of guile-json.
  (Invoking guix import): Document new `guix import cpan` command.

tests: import: Factorize utility function.

* tests/pypi.scm (mock): Move this...
* guix/tests.scm: to here.

import: Factorize utility functions.

* guix/import/pypi.scm (hash-table->alist, flatten, assoc-ref*,
  url-fetch, json-fetch): Pull procedures from here into...
* guix/import/utils.scm: Here and...
* guix/import/json.scm: Here.  New file.
* Makefile.am (MODULE)[HAVE_GUILE_JSON]: Add it.
* guix/import/gnu.scm (file-sha256): Move from here to...
* guix/hash.scm: Here.
* tests/pypi.scm (pypi->guix-package): Update mock module reference.

import: gnu: Propagate the key-download argument.

* guix/import/gnu.scm (gnu->guix-package): Pass the key-download
  argument on to gnu-package->sexp.

gnu: poppler: build with openjpeg and lcms

* gnu/packages/pdf.scm (poppler): build poppler with openjpeg 1.5 and lcms.

gnu: openjpeg: Update to 2.0.1.

* gnu/packages/image.scm (openjpeg): Update to 2.0.1.

gnu: Add openjpeg-1.

* gnu/packages/image.scm (openjpeg-1): New variable.

gnu: openjpeg: update home page URL.

* gnu/packages/image.scm (openjpeg)[home-page]: Update URL.

substitute-binary: Micro-optimize 'narinfo-sha256'.

* guix/scripts/substitute-binary.scm (narinfo-signature->canonical-sexp):
  Change "~a" to "~s" in error message.
  (%signature-line-rx): Remove.
  (narinfo-sha256): Use 'string-contains' instead of 'regexp-exec', and
  'string-take' instead of 'match:substring'.

records: Optimize 'recutils->alist' by avoiding regexps.

* guix/records.scm (%recutils-field-rx, %recutils-comment-rx,
  %recutils-plus-rx): Remove.
  (%recutils-field-charset): New variable.
  (recutils->alist): Adjust to use tests (string-ref line 0) instead of
  regexps.

base64: Inline arithmetic operations.

* guix/base64.scm (define-alias): New macro.
  (fxbit-field, fxarithmetic-shift, fxarithmetic-shift-left, fxand,
  fxior, fxxor): New aliases.

tests: Add missing copyright line.

* tests/lint.scm: Add missing copyright line for commit 907c98ac and
  others.

gnu: automake: Update to 1.15.

* gnu/packages/autotools.scm (automake): Update to 1.15.

gnu: git-manpages: Install under $out/share/man, not $out/share.

* gnu/packages/version-control.scm (git-manpages)[argument]: Install
  under $out/share/man, not $out/share.

gnu: Add git-manpages.

* gnu/packages/version-control.scm (git-manpages): New variable.

gnu: git: Update to 2.2.1.

* gnu/packages/version-control.scm (git): Update to 2.2.1.

gnu: libtool-2.4.4: Disable tests on MIPS.

* gnu/packages/autotools.scm (libtool-2.4.4)[arguments]: New field.