profiles: Add 'manifest-transaction'.

* guix/profiles.scm (<manifest-transaction>): New record-type.
  (manifest-perform-transaction): New procedure.
  (manifest-show-transaction): New procedure.
* tests/profiles.scm ("manifest-perform-transaction"): New test.

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

profiles: Add 'manifest-add'.

* guix/profiles.scm (manifest-add): New procedure.
* tests/profiles.scm (guile-1.8.8): New variable.
  ("manifest-add"): New test.

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

profiles: Add 'package->manifest-entry'.

Suggested by Alex Kost <alezost@gmail.com>.

* guix/scripts/package.scm (options->installable)[package->manifest-entry]:
  Move to (guix profiles).
  [package->manifest-entry*]: New procedure.
  Use it.
* guix/profiles.scm (package->manifest-entry): New procedure.
* tests/profiles.scm (guile-for-build): New variable.
  Call '%guile-for-build'.
  ("profile-derivation"): New test.

profiles: Switch to gexps.

* guix/profiles.scm (<manifest-entry>)[path]: Rename to...
  [item]: ... this.  Update users.
  (manifest->sexp): Rename to...
  (manifest->gexp): ... this.  Return a gexp.
  (lower-input): Remove.
  (profile-derivation): Remove 'store' parameter, and turn into a
  monadic procedure.
  [inputs]: New variable.
  [builder]: Turn into a gexp.
  Replace call to 'build-expression->derivation' with call to
  'gexp->derivation'.
* guix/scripts/package.scm (link-to-empty-profile): Adjust call to
  'profile-derivation', and wrap it in 'run-with-store'.
  (show-what-to-remove/install): Rename 'path' to 'item'.  Check whether
  ITEM is a package, and return its output path if it is.
  (input->name+path): Remove.
  (options->installable): Set 'item' to P.
  (guix-package): Adjust call to 'profile-derivation'.
* tests/profiles.scm (guile-2.0.9): Change 'path' to 'item'.

Merge branch 'master' into core-updates

Conflicts:
	guix/packages.scm

guix package: Allow removal of a specific package output.

Fixes <http://bugs.gnu.org/15756>.

* guix/profiles.scm (<manifest-pattern>): New record type.
  (remove-manifest-entry): Remove.
  (entry-predicate, manifest-matching-entries): New procedures.
  (manifest-remove): Accept a list of <manifest-pattern>.
  (manifest-installed?): Replace 'name' parameter by 'pattern', a
  <manifest-pattern>.
* guix/scripts/package.scm (options->removable): Return a list of
  <manifest-pattern>.
  (guix-package)[process-action]: Use 'manifest-matching-entries' to
  compute the list of packages to remove.
* tests/profiles.scm: New file.
* Makefile.am (SCM_TESTS): Add it.