FMSLogo Code

Fix some build breaks on Windows that was introduced in the previous revision that got the "Set Color" dialog boxes working on non-Windows platforms.

Enable the "Set Color" dialogs on non-Windows platforms.

Currently, only "Set Screen Color" actually works, but that's because the Logo commands for SETFLOODCOLOR and SETPENCOLOR are not yet implemented on non-Windows platforms.

Add missing #include directives to fix build breaks when USE_PRECOMPILED_HEADER is not defined.

Remove a TODO to enable WX_PRECOMP.
This has been done, but with a different precompiler symbol.

Fix the "test" target, which broke when "logo", "www", and "extras" were moved into separate subversion projects.

Fix build breaks on Windows that were introduced in the previous revision (getting CLEARSCREEN to run on GNU/Linux).

Implement ibm_clear_screen using wxWidgets so that it works on GNU/Linux.
This makes CS and the Reset button work correctly on GNU/Linux.

Move checkwindow() to a platform-independent portion of the code, since it uses pure wxWidgets API.

Rewrite checkwindow() to be platform-independent (using wxWidgets instead of win32 API)

Work around a problem that appeared on GNU/Linux after upgrading from wxWidgets 2.8 to wxWidgets 3.0.
For some reason, wxINVERT does not work in GTK (the lines it draws are invisible)