Examples for #:opaque and require/typed/provide
Move json tests to racket-test pkg.
Don't run special sandbox tests when the relevant libs are not available.
Create `unstable-debug-lib`, `unstable-pretty-lib`, `unstable-flonum-lib` packages.
Add `scribble-text-lib` package.
Add more correct dependencies for `racket-test`.
Fix unneeded R6RS dependency.
Disable broken contract test.
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