Clean up Mac OS GUI code

Include paths are updated to include the directory. It seems that
CodeWarrior will search for include files recursively, which means that
"error.h" may resolve to the wrong file (there are two). I am unsure of
the rules CodeWarrior uses to find header files.

Support for older versions of Universal Interfaces has been added.

The project code has been reworked after thoroughly reviewing Inside
Macintosh: Files. It is not complete, but it compiles, and the behavior
of the Save / Save As commands have been thought out more carefully.

lib/defs.h

@@ -23,6 +23,13 @@
 // Classic Mac OS. Header is part of Universal Interfaces & Carbon.
 #include <ConditionalMacros.h>
 
+// The target API macros do not exist until later versions of Universal
+// Interfaces. For example, they do not exist in Universal Interfaces 3.1, which
+// ships with CodeWarrior Pro 4.
+#ifndef TARGET_API_MAC_OS8
+#define TARGET_API_MAC_OS8 1
+#endif
+
 #elif __APPLE__
 
 // Newer apple systems, including macOS >= 10. Header is in /usr/include, or

lib/test.h

@@ -24,7 +24,7 @@ void Failf(const char *msg, ...) __attribute__((format(printf, 1, 2)));
 // invalid.
 const char *ErrorDescriptionOrDie(ErrorCode err);
 
-// Print information about completed tests and return the status code. 
+// Print information about completed tests and return the status code.
 int TestsDone(void);
 
 #endif