tidy up gui

Also improve the speed of compute-diffs by approximately 350x
(from 18+ seconds to about 50 milliseconds on the test case
that's currently failing)
make-traversal's optional argument is now ignored

Recent changes eliminated it, but it seems better
(for backwards compatibility) to leave it there but
ignore it
Redex: generation for judgment-form side-conditions

- enable generation for the above by compiling to
a disequation with "#f"

- wrap bare terms in relation definitons in
  side-conditions (require they not be "#f")
declare failing test should not have failed

This test started failing due to the additions of the calls
to clip, introduced in commit e6dc9c28b492d95.  The actual
difference is only 9 pixels out of about 100,000 relevant
pixels. Even better, here's the precise rgb values for the
mis-matched pixels (the alpha values don't change):

   (224 251 255) vs (229 255 255)
   (200 242 255) vs (205 247 255)
   (205 242 255) vs (210 247 255)
   (205 242 255) vs (210 247 255)
   (205 242 255) vs (210 247 255)
   (205 242 255) vs (210 247 255)
   (200 242 255) vs (205 247 255)
   (224 251 255) vs (229 255 255)
   (242 255 255) vs (247 255 255)

It isn't clear to me why clipping like this would have this
particular change, but I think it is safe to assume that
Redex shouldn't change in response to this!
like d9c81a593, but this time only 4 pixels
(and this time under linux, not mac os x)
Racket rename
fixed .ss name in title
Racket rename
Removing saltification compat
using bcrypt
Extending cookie support with expiration

Providing access to paths on id-cookies

Change PNR to limit checksum updating unless forced
Add take-while, drop-while to racket/list
adjust gc2's mutator language so that void-producing expressions
are allowed only in places where the value is discarded
remove ->address
add in documentation for plai/gc2
unbreak get-root-set
GCalc updates.

* Lots of racket-isms.

* Add ".rktd" to the sample file.

* Fix an old bug where the large display wouldn't get refreshed.
Fix renamed file in props.
Style changes.

No need to stick with the srfi-1 style of `lis' and `recur'.  I also
removed the srfi-1 comment since this code is straightforward.  (I keep
such comments if there's something non-trivial that was taken.)
fix plai tests