Replace ' chars with \u0027 in Android DTD
Call quotefordtd() from quoteforandroid()

This will provide all quoting for regular DTDs also in Android DTDs.
Add missing assert for test_unquotefromandroid()
Add unquotefromandroid()

This will allow roundtrip conversion for Android DTD files using Android
specific escaping and unescaping.
Add support for converting Android DTD to PO

Fixes bug #2480.

This will allow to do roundtrip tests for Android DTD files.