FMSLogo Code

Remove a #ifdef WXPURE by replaceing MessageBox with nearly equivalent wxMessageBox.
This is not exactly the same because the original used the deprecated MB_ICONQUESTION, which wxWidgets doesn't support.
This is a small step toward to a native GNU/Linux version of FMSLogo.

Add a regression test that SAVE displays a warning if run while the editor is open.

Replace some logic that copied a file with wxCopyFile.
This is clearer and probably faster and more correct.

Replace unlink with wxRemove.
This helps with porting FMSLogo to Unicode, as wxRemove works for both char* and wchar_t*.

Fix Bug #529; OPENREAD "clipboard no longer corrupts the line endings.

Use wxFileName::CreateTempFileName to create temp files.
This was done to be more portable, as the platform-specific logic for selecting a TEMP directory is now in wxWidgets, which, presumably is correct.

Replace remove() with wxRemove.
This will help in porting FMSLogo to support unicode.

Integrate changes from trunk, which were made to make porting to Unicode easier.

Fix some build breaks when compiling for Unicode.

Rework CStringNodeBuffer to clarify the difference between bytes and characters.
Although this currently makes no difference, it will help when porting FMSLogo to Unicode.