Cleanup of includes and related changes based on include-what-you-use diagnostics (#436)

Remove unused #define PERCENT_OF_SCREEN in MyWindow.h
Move structures for dir.c to dirdefs.h where they are used
Resolve S_CHAR vs S_CHARACTER in favor of S_CHARACTER and cleanup #defines
Fix  = vs == bug in FSDEBUG code in dir.c
Eliminate duplicate/unused constant definitions in gcr.c
Declare static internal function bytecmp in mkatom.c
Update many source and include files to include headers for what they use

src/keyevent.c

@@ -51,6 +51,7 @@ void Mouse_hndlr(void); /* Fields mouse events from driver        */
 
 #include "iopage.h"
 #include "ifpage.h"
+#include "miscstat.h"
 
 #include "bb.h"
 #include "bitblt.h"