[MERGE] Before actually using encoding need to check that Python has corresponding codec (v.3)

[John Arbash Meinel]

John Arbash Meinel has voted +1 (conditional).
Status is now: Conditionally approved
Comment:
I think it is important that we remove entries from the FakeCodec set so 
that we don't retain state between tests.

And you can simplify the cleanup with osutils.set_or_unset_env().


For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3Cene03h%24btf%241%40sea.gmane.org%3E