use racket/base instead of racket in queue
speed up graph constructors

- dont use generator
- use racket/base
- use unsafe-struct-ref and other unsafe ops
use racket/base and some unsafe ops
use racket/base
use racket/base; use unsafe ops; remove broke? parameter
speed up graph-fns-basic (esp scc)

- use racket/base
- use unsafe-ops
- don't use broke? parameter
- scc stack member check replaced with constant time hash lookup
clean up timing-test-scc; add zipped SCC.txt