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/mkcell.c

@@ -27,20 +27,16 @@
 */
 /**********************************************************************/
 
-#include "lispemul.h"
-#include "lispmap.h"
+#include "adr68k.h"        // for Addr68k_from_LADDR
+#include "allocmdsdefs.h"  // for alloc_mdspage, initmdspage
+#include "commondefs.h"    // for error
 #include "emlglob.h"
+#include "gcdata.h"        // for DELREF, GCLOOKUP
+#include "lispemul.h"      // for LispPTR, DLword, NIL, POINTERMASK, state
+#include "lispmap.h"       // for S_POSITIVE
 #include "lspglob.h"
-#include "lsptypes.h"
-#include "address.h"
-#include "adr68k.h"
-#include "cell.h"
-#include "gcdata.h"
-
-#include "mkcelldefs.h"
-#include "allocmdsdefs.h"
-#include "commondefs.h"
-#include "gchtfinddefs.h"
+#include "lsptypes.h"      // for dtd, GETWORD, GetDTD
+#include "mkcelldefs.h"    // for N_OP_createcell, createcell68k
 #ifdef DTDDEBUG
 #include "testtooldefs.h"
 #endif