* doc/guix.texi (Invoking guix deploy): Add section describing
prerequisites for deploying as a non-root user.
* guix/remote.scm (remote-pipe-for-gexp): New optional 'become-command'
argument.
(%remote-eval): New optional 'become-command' argument.
(remote-eval): New 'become-command' keyword argument.
* guix/ssh.scm (remote-inferior): New optional 'become-command'
argument.
(inferior-remote-eval): New optional 'become-command' argument.
(remote-authorize-signing-key): New optional 'become-command' argument.
* gnu/machine/ssh.scm (machine-become-command): New variable.
(managed-host-remote-eval): Invoke 'remote-eval' with the
'#:become-command' keyword.
(deploy-managed-host): Invoke 'remote-authorize-signing-key' with the
'#:become-command' keyword.
* gnu/machine/ssh.scm (machine-ssh-configuration): Add 'system' field.
(managed-host-remote-eval): Pass 'system' field to 'remote-eval'.
(machine-check-building-for-appropriate-system): New variable.
(check-deployment-sanity): Add call to
'machine-check-building-for-appropriate-system'.
* doc/guix.texi (Invoking guix deploy): Describe new 'system' field.
* guix/ssh.scm (remote-system): New variable.
* guix/remote.scm (remote-eval): Use result of 'remote-system' when
lowering the G-Expression.
(remote-eval): Add 'system' keyword argument.
(trampoline): Return a <program-file> rather than a <scheme-file>.
Fixes a regression introduced in 386857748097619b3b75a7bf93677b6aa742d03c.
* guix/remote.scm (remote-eval): Use 'append-map', not 'map', for
'derivation-input-output-paths'.
* guix/gexp.scm (lower-inputs): Return either <derivation-input> records
or store items.
(lower-reference-graphs): Return file/input pairs.
(<lowered-gexp>)[sources]: New field.
(lower-gexp): Adjust accordingly.
(gexp->input-tuple): Remove.
(gexp->derivation)[graphs-file-names]: Handle only the
'derivation-input?' and 'string?' cases.
Pass #:sources to 'raw-derivation'; ensure #:inputs contains only
<derivation-input> records.
* guix/remote.scm (remote-eval): Adjust to the new <lowered-gexp>
interface.
* tests/gexp.scm ("lower-gexp"): Adjust to expect <derivation-input>
records instead of <gexp-input>
