* guix/scripts/hash.scm (show-help): Add --recursive.
(%options): Likewise.
(guix-hash)[file-hash]: New procedure. Honor --recursive.
Use it.
* guix/nar.scm (write-file): Add missing field to the &nar-error
condition raised upon unsupported file type; change its message to be
more descriptive.
* tests/guix-hash.sh: Add tests with -r.
* doc/guix.texi (Invoking guix hash): Document --recursive.
* guix/scripts/hash.scm (guix-hash)[eof->null]: New procedure.
Use it to convert the EOF object to the empty bytevector.
* tests/guix-hash.sh: New file.
* Makefile.am (SH_TESTS): Add it.
* guix/scripts/hash.scm: New file.
* Makefile.am (MODULES): Add it.
* po/POTFILES.in: Add it.
* doc/guix.texi (Invoking guix hash): New node.
(Defining Packages): Add a cross-reference to the 'Invoking guix
hash' node.