add necessary includes and forward decls in public header files (bug #55277) * load-save.h: Include ovl.h for full octave_value_list definition, delete forward decls that are now declared by inclusion. * oct-hist.h: Include ovl.h for full octave_value_list definition, add forward decl of octave::interpreter. * pager.h: Add forward decl of octave_value_list. * settings.h: Add forward decl of octave_value, include cstddef for size_t. * pt-tm-const.h: Include pt-mat.h for full octave::tree_matrix definition.

--- a/libinterp/corefcn/settings.h	Sun Dec 30 13:18:05 2018 -0800
+++ b/libinterp/corefcn/settings.h	Sun Dec 30 13:26:33 2018 -0800
@@ -25,6 +25,9 @@
 
 #include "octave-config.h"
 
+#include <cstddef>
+
+class octave_value;
 class octave_value_list;
 
 namespace octave