Untag specs fixed by jruby/jcodings@ae2b92b.
Remove commented debug logging.
Fix IO/File.open to return the block value rather than the IO.

This makes isatty/tty specs 100%.
Remove experimental and now defunct try_nonblock library.

See https://bugs.ruby-lang.org/issues/5138
Loosen restriction on $stderr to just #write.
Reimplement IO#write_nonblock. 100% on CI specs.
In contrast to MRI, set streams blocking again.
Pass given class through to popen.
Return result of yield or io.