Unicode support for text I/O

This means adding Unicode encoding/decoding for Text I/O handles.

Consensus was that Text I/O should always use the current locale encoding.

You can elect to have no encoding by opening in binary mode, but that's all.

Presumably this will need the ability to convert between arbitrary encodings internally, so it would make sense to also expose this functionality as a library.

Trac metadata

Trac field	Value
Version	6.10.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	high
Resolution	Unresolved
Component	libraries/base
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