Support images in check failure output

[aymanosman]

Fixes #130

This PR makes rackunit print values directly, as opposed to turning them into strings first.

[rmculpepper]

When I try running the following program in DrRacket, I still get the picts printed as #<pict> in the output. Is it working for you?

#lang racket/base
(require pict rackunit)
(check-equal? (circle 10) (circle 20))

[aymanosman]

You are right, thanks. I broke the implementation whilst fixing a merge conflict. Should be fixed now.

[samth]

I think this merge broke the previous merge -- see the tests now failing at: http://drdr.racket-lang.org/57762/cs/racket/share/pkgs/rackunit-test/tests/rackunit/standalone.rkt and http://drdr.racket-lang.org/57762/cs/racket/share/pkgs/rackunit-test/tests/rackunit/run-tests.rkt

[samth]

This change broke the rackunit-fancy-runner rackunit-pretty-runner package, which was using the private info-value->string function. Would it make sense to restore that function using the new code written in this PR?

[aymanosman]

@samth Can't seem to find that package anywhere.

[samth]

@aymanosman it's here: https://pkgs.racket-lang.org/package/rackunit-fancy-runner

[samth]

I see that you couldn't find it because I wrote the wrong name, sorry about that!