fix: force StringIO encoding to ASCII_8BIT

[pparidans]

render method in Prawn::Document uses a StringIO instance as default output.
But on JRuby for Windows this class uses a default encoding of UTF-8 instead of ASCII_8BIT, than breaking inrender_header method by pushing non-UTF characters in the StringIO instance.

It was also breaking a lot of tests (I'm not listing all of them. Should be at least every in-memory render calls).

Environment:

• Windows 7 x64 SP1
• Java 1.7rev51
• JRuby 1.7.10

[practicingruby]

Hi, I think we're seeing a few bugs related to encodings in JRuby, so this may help. I'll take a closer look at it in a few days. Thanks!

[pparidans]

Actually, I also test it on OS X: all tests are passing (without this modification) for both MRI 2.1.0 and JRuby 1.7.10. Didn't checked yet on Linux.

If you need more tests from a Win machine, let me know!

[practicingruby]

If you don't mind testing something unrelated and have Adobe Reader XI handy, you could try simply opening the PDF generated by the code in the description of this ticket and see if you get an error: #631

We've been unable to reproduce on OS X.

[pparidans]

Done!

BTW, I'm not sure that it would be related to the current issue because generate and render_file use a File object and not a StringIO. And I never had any problem when directly generating pdf to file.

[pparidans]

I still need to run tests for this modification with a MRI implementation on Windows to check that tests are still passing on this configuration.

Anyway, Travis-CI seems to be happy! 😎

[practicingruby]

No, I doubt #631 has anything to do with this issue. We were just lacking windows testers 😁

[pparidans]

Go ahead! If you need more Windows' tests, I would happily help!

[practicingruby]

I'm going to go ahead and merge this, but I don't have a way to reproduce it myself. If it causes any problems I'll need to revert first and ask questions later.

[pparidans]

Thank you @sandal ! :)

[practicingruby]

@pparidans: Because your pull request was accepted, you now have commit access to all of prawnpdf's repositories. Please see the link below for contribution guidelines, and thanks again!

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