directory-list: always sort results

Consistently sorting shouldn't cost much relative to the
cost of `directory-list' (except for the path->bytes conversion?),
and it makes directory traversals (including archive packaging)
more deterministic across runs and platforms.

(Eli suggested this a long time ago.)
add `path<?' and `symbol<?'

These comparisons are useful for sorting while avoiding the overhead
of conversions to bytes or strings.

Having `path<' reduces the cost of sorting in `directory-list'.
GUI package manager: catch and report errors
official catalog server: allow package addition via update API
package catalog server: fix "pkgs-all" query
first cut at script to push PLT packages to pkg.racket-lang.org