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

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

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

Fixes bug #2480.

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