Make register snapshot test-cases work on Windows.

The register tests use an append register which collates using "\r\n" on
Windows. The input and state check files would always be converted to
"\n" and thus fail when the test buffer contains a "\r\n" somewhere.
Use assertEquals for better JUnit integration

Eclipse has a nice "String compare view" for each failed result, making
it far easier to detect newline problems.

The only downside is that te "expected, got" messages are duplicated,
first Vrapper's with its cursor marker, then JUnit with it's string
compare message.
Use Mockito magic instead of dummy UIService impl

SnapshotTests implemented UserInterfaceService when all it wanted to do
was to print any error messages. Any changes to the interface would thus
break the tests.

Use Mockito's doAnswer and Answer API instead.
Use Mockito magic to print error messages

Use Mockito's doAnswer and Answer API to handle the setErrorInfo method
of the UserInterfaceService. This way, we don't need a (fragile) stub
just to run our tests.
Javadoc for snapshot tests.