Implement DTDHandler support for ExpatParser.

Every time a third-party developer gets their DefaultHandler method signatures
wrong (making it impossible for us to call them), they see this in the log and
complain that SAX parsing is broken on Android:

  WARN/ExpatReader(704): DTD handlers aren't supported.

This patch adds that support -- even though no-one wants it -- so we can get
rid of the irrelevant log message.
4 files changed