Change po2dtd tests since " is now escaped in DTD
Add some new tests in test_roundtrip_quotes()
Change print in roundtripsource() in order to ease reading when test fails
Add test for single quote escaping in Android DTD
Add parse and convert back test with single quote escaping in Android DTD
Add test for double quote escaping in Android DTD
Add parse and convert back test with double quote escaping in Android DTD
Add roundtrip tests for Android DTD