fix #99 do not close stream when autoclose is disabled in yaml generator/parser

[vboulaye]

fix for #99
I reported the checks done before closing the enclosed writer from the WriterBasedJsonGenerator in jackson core to the YamlGenerator
A similar check was apparently also missing in the parser, I copied the one from the ReaderBasedJsonParser to the YamlParser
I also copied the original comments that explain the reasoning behind the checks (even though they date from 2008, they still apply)

[cowtowncoder]

Looks legit, thank you very much for contributing this!

Before I merge the fix to be included in 2.9.8 (thank you also for making this against 2.9 branch, makes my life easier), one last thing: unless I have asked for and received CLA (apologies if so), we'd need it from:

https://github.com/FasterXML/jackson/blob/master/contributor-agreement.pdf

(or, if you need corporate-CLA for work done on behalf of a company, there's alternative)

and the usual way is to print, fill & sign, scan, email to info at fasterxml dot com.
One CLA is enough for all Jackson projects, contributions, so it's just one-time hassle.
Once that is done, I'll merge this in .

Thank you again!

[vboulaye]

I just sent the CLA.

By the way thank you for everything you do on this project, I'm glad I could help a little bit!

[cowtowncoder]

Thank you for fixing this!