Split up tests for quotefordtd() and unquotefromdtd()
Add commented code for escaping and unescaping < and > characters
Add new asserts in test_unquotefromdtd()
Add assert in test_quotefordtd() for checking singlequoting around string
Add docstring to test_quoteforandroid()
Change assert in test_quoteforandroid() for checking new behavior
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.