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/lib/DtTerm/TermPrim/TermPrimBuffer.h

@@ -662,6 +662,17 @@ _DtTermPrimBufferSetInSelectionFlag
     short       row,
     TermLineSelection     state
 );
+
+extern void
+_DtTermPrimBufferSetSelectLines
+(
+    TermBuffer tb,
+    short beginRow,
+    short beginCol,
+    short endRow,
+    short endCol
+);
+
 #ifdef	__cplusplus
 } /* close scope of 'extern "C"'... */
 #endif	/* __cplusplus */