Fix test_Cursor29 for libclang 3.1 and earlier.

On libclang 3.1 and earlier, given:
	enum test { a };

the test.semantic_parent and test.lexical_parent properties return
an UnexposedDecl cursor instead of a TranslationUnit cursor. This
changes those tests to use `a` instead of `test` as the cursor that
is used, which works as expected.