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* Created screenwindow.cpp, which abstracts the windowing framework from the language engine.
* Renamed ibmturt.h to ibmterm.h to match the name of the .cpp file.
* Refactored g_OpenFiles in files.cpp so that it kept track of if the FILE* was opened for binary, rather than using an unportable check.
* Split Borland OWL parts out of mainwind.cpp and into mainframe.cpp.