Add XRC testing to sdi_test project

Description:

Currently there's no coverage of XRC in the sdi_test project. It should be fairly straightforward to create additional functionality in either mainframe.py, mainframe.rb or mainframe.cpp that could load and display XRC dialogs. In fact, we could probably add it to all three -- it might be useful someday to have code in all three languages that creates forms from XRC.

[Randalphwa]

We already do this for C++ (xrc_python_dlg), but it would make sense to also add that to python/ruby/perl, though it's a low priority.