bootstrap: sync with upstream.

* build-aux/bootstrap.in: sync with upstream.
* bootstrap: Regenerate.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
bootstrap: support rockspecs in $buildreq, and --luarocks-tree.

* build-aux/bootstrap.slingshot (require_rockspecs_req)
(slingshot_rockspec_error, slingshot_split_buildreq)
(slingshot_check_rockspecs): New functions.  Add support for
checking versions of rockspecs listed in $buildreq.
(slingshot_check_rockstree_path): New function. Warn if a
custom rockstree is passed, but not added to PATH.
(slingshot_options_prep, slingshot_parse_options)
(slingshot_option_validation): New functions.  Add support for
--luarocks-tree=DIR.
* bootstrap: Regenerate.
* NEWS: Update.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>