- rename old `racket/stream' to `racket/sequence', and adjust
to avoid stateful iterations
- add a new `racket/stream' library with a `strean-cons' that is based
on SRFI 41
- adjust `for' and some sequence constructors like `in-range' to
work more directly with streams
* Another big chunk of v4-require-isms
* Allow `#lang framework/keybinding-lang' for keybinding files
* Move hierlist sources into "mrlib/hierlist", leave stub behind
svn: r10689