DataTransferer is currently relying on private sun.io APIs. Once JSR 51 is
putback, it should be rewritten to use the new public APIs instead. This will
improve data transfer performance significantly, and will also ensure that we
don't attempt unsupported character conversions in some locales.

The following dependencies should be removed:
  * Use of sun.io.CharacterEncoding.charsetIterator in
    DataTransferer.supportedEncodingsIterator.
  * Use of sun.io.CharacterEncoding.aliasName throughout the class.
  * Use of sun.io.CharToByteConverter in DataTransferer.ReencodingInputStream.

In addition, CharacterEncoding.charsetIterator itself can be removed.
DataTransferer is the only client of the function.

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In addition, the new java.nio classes CharBuffer and ByteBuffer should be fully
supported by the data transfer subsystem. They should be of the same order as
Reader and InputStream. This will require a series of API changes.