Kill most warnings in lib/DtTerm.

Mostly missing headers, explicit parentheses and new prototypes.

Some Caveats:
* I haven't compile-tested the SVR4 getpty file, it might need another tweak
* There were operator precedence bugs in TermPrimCursor.c and TermPrimRender.c
  (^ vs. !=).  This might change behaviour, but at least I haven't experienced
  any crashes ...
* This adds a little more dependencies for include ordering, but unless we
  want to play the "headers that include headers that include headers..." game,
  this is unavoidable.

cde/programs/dtterm/DtTermMain.c

@@ -37,6 +37,7 @@ static char rcs_id[] = "$TOG: DtTermMain.c /main/19 1999/09/17 13:26:34 mgreess
 #include <dlfcn.h>
 #endif /* sun */
 #include "TermHeader.h"
+#include "TermPrim.h"
 #include "TermPrimDebug.h"
 #include <fcntl.h>
 #include <sys/types.h>