wxutil::TreeModel variables are stored as wxObjectDataPtrs intead of raw pointers

Should reduce potential for errors in IncRef/DecRef calls.
Added missing Automake-generated scripts
Fixed crashes in ModelSelector on Linux

- TreeView is not created until after the models list is populated and the
  TreeModel is ready to be associated. Leaving the TreeView without a model
  seems to cause a crash when the progress dialog triggers idle event
  processing.
- Removed AssociateModel(NULL) call on shutdown, since this causes an immediate
  crash on Linux. Instead the TreeView is simply destroyed.
Merge branch 'master' of https://github.com/orbweaver/DarkRadiant