tests/node_test:

Don't use unicode with StringIO objects; this issue was fixed in Python
2.7.3, but is still an issue for other 2.7 versions.

(For example, OSX 10.7 ships with 2.7.1.)

This change simply makes the tests more fault tolerant in more diverse
environments.
Merge pull request #113 from larsbutler/no-stringio-unicode

No unicode + StringIO in tests

[r=micheles] [f=*trivial]