yum shell: broken readline functionality

Hi!

This patch, that unconditionally replaces sys.stdout by a streamwriter
broke the readline functionality of yum shell:

http://yum.baseurl.org/gitweb?p=yum.git;a=commit;h=259814b433c733430b0560f38d153aaa6038f633

Maybe readline checks if sys.stdout is a tty?

Cheers,
--leo
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e-mail   ::: Leo.Bergolth (at) wu-wien.ac.at
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