Stream individual strings for expansion to Racket.

This ends up being pretty painful, primarily because
there's no way to simulate the effect of EOF in the
shell.

Also, it doesn't seem to fix the horrible slowness
of the tests.
Merge branch 'master' into streaming
speed up test_eqv

(not really worth it, it seems, this saved 3 seconds)
Properly handle interesting identifiers under quote.
Merge remote-tracking branch 'origin/streaming'