* guix/store/database.scm (sqlite-register): Add #:schema. Parameterize
'sql-schema' based on this.
(register-path): Add #:schema and pass it to 'sqlite-register'.
* guix/store/database.scm (add-reference-sql): Remove nested SELECT.
(add-references): Expect REFERENCES to be a list of ids.
(sqlite-register): Call 'path-id' for each of REFERENCES and pass it to
'add-references'.
* tests/store-database.scm ("register-path with unregistered references"):
New test.
This allows 'guix' commands to talk to a remote store over SSH.
* guix/store.scm (connect-to-daemon)[connect]: Call 'resolve-interface'
for unknown URI schemes.
* guix/store/ssh.scm: New file.
* Makefile.am (MODULES): Add it.
* doc/guix.texi (The Store): Document it. Mark remote access as
experimental.
